The whole thing with skirts and dresses, at least to me, is about "emphasizing traditional gender roles" and there are a lot of people who subscribe to that theory-there have been several episodes of Wife Swap where one of the families was skirts-only for the females. When the rules change happened, the wife who went there said that the girls would be wearing pants, and they adamently refused. After you do something for so long, it sort of becomes you, I suppose.
When I was younger and I wore skirts/dresses, I always had to wear either bike shorts or bloomers (if it was a longer dress) in order to maintain modesty. That's the way it was (I doubt it was with bloomers though) for most people when I was growing up and in the church. Nowadays, the really rowdy girls just end up wearing pants, or they're told that they can't play around and go tumbling in the Narthex.