I’m going to bring up (invent?) the concept of subjectification.
As in, people gravitate to the characters given the most depth, complexity, and satisfying interactions for their shipping needs, because those characters are most human, and we want the realest characters to play with.
In a lot of media, the most depth gets handed to male characters.
And, oftentimes, even when the screentime and depth and interactions are granted equally well to female characters, there can be a level of, for lack of a better word, dis-authenticity to those female characters: they are pared down, washed out, or otherwise made slightly less themselves than they could be, in the interest of making them decorative, or likeable, or “good,” or keeping them from upstaging or emasculating their male companions, or just that the writer whose job it is to write them doesn’t know how to write women the way they write men.
And you get the characterization equivalent of that comparison chart where so many animated female characters have the same facial features because the animators and designers are so worried about not letting them be ugly.
When you have a group that’s allowed to be themselves, warts and all, and another group that has to be decorative at all costs, the impression given on some level is that the decorative quality is making up for a shortcoming. That they wouldn’t be enough in their own right.
And sometimes that cost is authenticity. The interesting, striking, awe-inspiring, bold and glorious unapologetic selfhood that draws the viewer most particularly to those characters who are unapologetic in their particular existence, standing clear of the generic and bland and unchallenging “safe” appearances.
It is authenticity, not beauty, which powers subjectification. The love for a character, not because they are perfect, but because they are them.
They can be pretty, sure. They can be sweet. But being pretty and sweet is not a replacement, and too many female characters have been written by writers who think it is, while the interest—in appearance, in personality, in interactions, in plot development—goes to the men.
And when that happens, well. Surprise, surprise, that’s where the shipping goes.