There's certainly a "thrill" or "exciting" element to it, if I'm being completely honest. But that's only a component, I think a large part of it is that I want to look sexy and pretty. Why do I want to look like a girl? I've got no clue, it just feels fun. The better I can put into my presentation (as well as create new outfits) the better the experience. It's not just because girl's have more options (although I do like expressing more of a fashion aware side in my femme clothing), but it is explicitly tied to mirroring the female image. If the look isn't tied to what I think of as female attire, I don't have an interest in it.
