It is axiomatic that some women look more delicious in skirts and others do in trousers.
That point aside, surely trousers are infinitely more sensible than skirts?
I know that not everyone flies the 747 but just try coming down the upper deck escape chute in a skirt and see how your nylon undies burn themselves on to your nether regions. Were I a girl, there's no way I would want to jeopardise my enjoyment of life by wearing a skirt as flight crew.