Well... going back to the roots, skirts and dresses are traditionally women's clothing whereas trousers are men's. For some odd reason, today it is acceptable for women to wear trousers but if men wore dresses or skirts, they're labeled 'crossdressers'. Double standards of the stupid society. But when it comes to romantic attraction, men obviously get attracted to women who look more feminine (that is, those who wear skirts or dresses) than the others (who wear trousers). its as simple as that.