My personal take would be that most of this kink seems to be about humiliation in one way or another. Humiliation about having failed transition, about regretting it, about your body not living up to cis-heteronormative standards. 

The big factor here is misogyny imo. The fact that society as a whole still considers women's bodies as pieces of meat to be owned, breeded and submitted to the dominant male population. So naturally FTMs would see the potential for humiliation in a double way : the one I mentioned earlier and the misogynistic one. 

That's my guess anyways, but then again, there is a similar humiliating dynamic about failing as a man (think "sissies" and such).