Here's a quote:
The original Twitter discussion [that prompted the article] was about love triangles in YA fiction (love ‘em or hate ‘em?), which spurred me to think about the trope as a whole: why does it have to be combative? So many books use the triangle to push plot but would never consider letting the three characters in question come together. [more...]
It was a curious experience for me to read this article by Ms. Mandelo a day after re-reading the Song of Songs, which is Solomon's. It is as if I stepped from one universe into another.
I'm not going to focus on the moral issues involved here, particularly the issue of depicting kinky relationships in stories aimed at older children (what the "YA" label actually means), because covering that thoroughly would require a great deal of time and space and would carry the conversation into a realm different from the one I'm interested in at the moment. Instead, I'm going to focus more heavily on the artistic matters.
The brief answer to the question Ms. Mandelo poses is, because ending a love triangle with a three-way destroys the plot (or subplot) and betrays the reader.
Love triangles are of perpetual interest and popularity in fiction for at least two reasons: first, they touch on common human experience with which a large number of readers can relate, and second, they produce tension by creating a situation--a competition of sorts--that at least one character must inevitably lose. The build-up in that tension, with all the opportunities for shippers to argue rancorously on the Internet over who should lose and who should win, creates the pleasure of reading about love triangles. Twilight is interesting largely because Bella cannot have both her vampire lover and her werewolf lover. Girl Genius is interesting partly because Moloch von Zinzer cannot have his McNinja girl, his bucktoothed thief girl, and his creepy minion girl. He must choose, and choose wisely, for just as the true girl will give you life, the false girl will take it from you.
Take any generic Japanese harem comedy as a further example. Basically an exaggerated love triangle, the harem comedy is a story in which three to seven beautiful but eccentric girls are trying for improbable reasons to latch onto one erstwhile luckless loser. The harem comedy is interesting and entertaining precisely because only one girl can get the guy in the end; if it were a literal harem rather than a harem comedy, there would be no plot. If the story ended with the characters deciding to have a four-way, or an eight-way, it might be kinky, but it would be a dissolution rather than a resolution to the storyline, because the storyline is about one girl getting a guy--or perhaps more accurately, one guy choosing the right girl--and to end the story in such a way that the difficult choice does not have to be made, is cheating. It is a letdown. It is anticlimactic. This is because harem comedies, although they have a tendency to get mired in anatomical gags and sexual hijinks, are when stripped bare (so to speak) basically boy-meets-girl stories. They are love stories. And love stories are by nature exclusive and monogamous. More on that a little later.
Take Ranma 1/2. Please. How different would the story be if Ranma, instead of constantly fending off unwanted advances and trying awkwardly and halfheartedly to forge a relationship with the girl next door, simply made all comers, both and female? Again, kinky, but no plot. Susan Napier in her collection of essays on Japanese cartoons, Anime, has a chapter on Ranma 1/2 in which she makes a complaint somewhat similar to that made by Ms. Mandalo: Napier complains that Ranma 1/2, even though it constantly depicts characters violating boundaries, particularly boundaries surrounding sex and gender roles, does not do enough to undermine traditional Japanese views of gender, but instead ends up confirming them. I believe Napier has missed the point; a comical show like Ranma 1/2 cannot help but confirm traditional gender roles because the plot hinges on the protagonist's unintended transformations back and forth from male to female and the social discomfitures these transformations cause. If all the social norms were swept away, Ranma's accidental appearances in drag and other embarrassing moments would have no ability to shock and therefore no ability to amuse. Without social conventions to violate--and thereby pay homage to--Ranma 1/2 could not be funny. If Ranma did not care about his masculinity, he would not be embarrassed and the viewer could not laugh at him. Ranma 1/2 can only maintain its bouts of comedic boundary-transgression by simultaneously reinforcing the boundaries it transgresses, because it is dependent on those boundaries. Without social boundaries, there would be no conflict in Ranma 1/2, no humor, and no story. Similarly, if the "combative" elements were removed from a love triangle, there would be a kinky three-way relationship, but no conflict and no story.
When I think of stories containing relationships that might be called polyamorous, the first thing that springs to my mind is Paint Your Wagon, a so-bad-it's-good musical filmed near my home town (and entrenched in an annual celebration there), starring Lee Marvin and Clint Eastwood, neither of whom can sing. The story takes place in a California gold rush town, No-Name City, where there are no women until a Mormon arrives with two wives. After an Irish miner complains, "It's no fair you havin' two of what the rest of us ain't got none of," the Mormon agrees to auction off one of his wives, and she ends up with Lee Marvin's character. While Marvin is on a mission to kidnap some French prostitutes to populate No-Name City's new house of ill repute, he leaves his wife in the care of his pardner, Clint Eastwood, who promptly falls in love with her. On Marvin's return, the three of them all decide to be married together, and this unusual situation leads to most of the strained jokes after the intermission. Yet again, Paint Your Wagon is ultimately a love triangle; in spite of its intentionally boundary-violating premise, which again forms the basis of the humor, the ultimate question to be answered is which guy gets to keep the girl at the end of the film.
I am convinced romance is at its heart monogamous. This would seem to be best in tune with our biology; romance is about sex, and sex is our method of reproduction, and sexual reproduction can only occur between two people. But besides this, romantic desire itself seems to have something of exclusivity about it. The aforementioned Song of Songs, written in a society where polygyny was generally accepted, necessarily has a monogamous bent when it describes romantic love:
As a lily among brambles,
so is my love among maidens.
My dove, my perfect one, is the only one,
the darling of her mother,
flawless to her that bore her. (NRSV)
Romantic passion inspires vows of fidelity and exclusivity. When lovers describe what they love about one another, they emphasize uniqueness.
I am not claiming, of course, that only chaste stories leading to happy marriages can make moving love stories. I am much moved by the story of Abelard and Heloise, a real-life tragic tale as full of melodrama as any bodice-ripper, but which is basically about a tutor fornicating with his student. I am also much moved by the story of Tristam and Isolde, which is about a knight committing adultery with his lord's wife. I am moved, too, by Romeo and Juliet, which is the story of silly teenagers having a hasty, secret wedding and then offing themselves. I am even rather moved by Romeo x Juliet, which is the story of silly teenagers having a hasty, secret wedding and then offing themselves...IN SPACE!!! Also, in that version, Juliet is a superheroine.
But compare those, which are about exclusive love (even the ones with complications like unwanted marriages), to, say, Stranger in a Strange Land, a novel by science fiction's original advocate of polyamory. I don't mean compare the style, of course. I mean compare the quality of the stories, specifically the love stories. In Stranger, Robert Heinlein takes the love triangle and intentionally twists it. More than one woman is in love with Valentine Michael Smith, and the reader naturally expects that Mike will have to choose between them, but the story takes a turn when Mike finally makes one of the girls in the pool--and we never find out which girl it is. Heinlein purposely refrains from naming her. Her identity is unimportant because denying the exclusiveness of romance and opening the story to polyamory means the lovers cannot be unique to each other. If this were a book about the exclusivity of love, Heinlein could never have gotten away with neglecting to name the girl. Her identity, her person, would have been everything.
This is a pristine example of exactly what I was talking about above: to conclude a love triangle in this way is to destroy the plot and betray the reader. In this case, Heinlein did it on purpose as a sort of twist, but the story that develops from there, whatever else it may be, is decidedly not a love story. It is more like an anti-love story: it makes the claim that life would be happier if all the things that go into love stories were done away.
The kind of attitude that leads to the championing of polyamory is, I'm inclined to believe, of the sort that will inevitably lead to a lack of romance in fiction rather than an increase. At the end of her article, Mandelo mentiones sf author Nalo Hopkinson as one who approves of Mandelo's call for more polyamory. Some time ago, I had in my possession an interview with Hopkinson featured in the Novel and Short Story Writer's Market. I no longer have that volume, but I remember the salient parts. Hopkinson argues that exclusivity in sexual relationships is absurd, akin to making arbitrary taboos dictating that people can only eat in certain rooms with certain other people at certain times of day.
I don't know what this business is about rooms and times of day, and I note, looking at the news articles about obesity, that casually eating what we want when we want where we want with whom we want hasn't exactly been the best thing for our health, but that doesn't matter because the analogy is invalid; eating, at least when engaged in rightly, is a pleasurable activity that keeps the human body in good health, whereas sex is a pleasurable activity that produces other human beings and so should be expected to be freighted with peculiar moral obligations and maybe even some mystical mummery. But more importantly for this particular essay, Hopkinson's depiction of sex is decidedly unromantic. Good sex, as she depicts it in this interview, is the orgasmic equivalent of junk food--it is utterly casual and without meaning, and once again the identity of the other person is of little importance.
So, to the question of why more love triangles don't end in three-way polyamorous relationships, the answer is, because that is not a love triangle.