I've been asked the same question, basically "why wear something that's not designed for you", and tried to explain that not everything is done for the sake of appearing female, that some things (like wearing panties) are done for the sake of feeling feminine. We may want to pass as female or feel girly or both, but they're not always going to happen together.
I guess if we're always supposed to wear what's practical, we should all be wearing those futuristic unisex jumpsuits from the 24th Century.
