It's simply easier when girl's names and boy's names match up to their gender.
Take "Dakota" for example...how can I tell it's a girl or a boy...c'mon...it's the way we've been programmed and I see nothing very wrong with that. It simply makes subconscious identification easier. I don't know about the Trans situation, though, mostly they change their names, anyways. You don't have a child expecting s/he might be transgender...although maybe now it's different.