I think that for the most part, players choose the gender they prefer their character to present as and aren't all that interested in wearing clothes of the opposite sex aside from, understandably, the pants that are often locked to males while women get what feels like an excessive number of shorts in place of them.

While that is indeed frustrating, there isn't a lot of demand for men being able to wear dresses or skirts, especially not the ones from the eastern online store sets that are incredibly rare to see being used in game.