Again, the reason is development time. All these female-only clothes are going to need to be redesigned to be able to fit male characters. It's a lot of work, and it is work that would be done for a pretty small group of people (mostly attention-seekers, a few honest crossdressing enthusiasts).
Missed that boat - the aesthetic design is ALREADY completely ruined, and has been since the glamour system was implemented. Since it's already FUBAR'd, there's not a lot of harm in opening the floodgates further. :P
