I'm either aspie or hfa (not yet diagnosed, but I'm fairly sure I'm at least one of them), and also at least slightly cute.
But I think to some degree attractiveness is as much a personality and attitude thing as a physical thing - ok, some people are obviously aesthetic or ugly, going by the generl meaning of the word - but most fall somewhere in between, and the main difference tipping them one way or the other is their outlook. A confident, happy woman usually looks prettier than a depressed or insecure one - take actresses, for example. It's a general public assumption that most famous actresses are attractive, yet look carefully at their faces. There's not a lot separating them structurally from 'normal' women. Part of it is lighting and make-up, but a lot of it is just that they know how to exude confidence. So perhaps part of the problem is that the women you've seen are 'giving off a bad vibe'? After all, having a social dysfunction can be discouraging, and also, having an asd often means we don't portray facial expressions and body language in regular ways.
Or, it's possible there really is a tendency towards people on the autism spectrum not being generally aesthetic. Or you've just not met any attractive asd women yet. Just to list all the possible theories. 