I wonder if girls loving girls in this way, sans sex, reinforced the image of women--good ones, that is--as pure and untainted. Of course society wants them to have hearts capable of loving and caring... but it baulks at the notion of them getting sexual experience. A crush on a boy could be equally innocent, but maybe the general failure to recognize the possibility of female sexual intimacy made crushes on girls seem extra safe/pure, and therefore a good thing to stick in stories. This would go along with what you were saying about the prostitute and the fallen woman being the main evil ends for women.

That's interesting about crushes being regarded as silly. It's funny how society gets an idea in its collective head ("young people's crushes are silly"; "siblings dislike each other") and then runs with it. I mean there are always instances in which the generalization is true, but definitely not in the truth-universally-acknowledged sense.