I honestly don’t know. The impression I get (and it’s only that, I haven’t polled anyone) is that “crossdresser” is used more by people who don’t identify so much with the “boy” part of “femboy”. i.e. They may be older, or don’t have a lithe boyish physique. And to my mind anyway, it carries more of an erotic connotation, whereas “femboy” seems more casual to me.

The trans community exists on the euphemism treadmill. We invent terms, those terms gain a negative connotation, so we invent new terms. Those develop a negative connotation.

That’s an interesting point.