hmm i think its almost a fetish you know? like, there are people who like a big top (like me) and there are people who like the typical stall "masculine" fur to be subby.
dont get me wrong there are people who love both, i honestly don't mind it sometimes but i think the majority prefer the more popular big/top small/sub..

maybe all your fur friends just think you look better on all fours XD :P

I think they enjoy the power they have too much an get use to having it. When that changes they don't work as well or they feel they loose part of themselves.

Another reason I think it could be is image. Some have broken down and gone the subby route but not without a lot of insistent work getting them there.

Little guys can definitely dominate :3 Just put up a pic with just such a thing...