The science was done on this by a shrink who saw these guys in his practice and described the phenomenon before he was canceled for pointing otu the truth. There are almost exactly only two classes of guys who troon out:

• Homosexuals who hate they are, for whatever reason, gay, and decide consciously or not that it's better to be a woman and
• Autogynephiles who have a powerful paraphilia. these ones are, by the way, these days, all led down the road to traindom from sissy and hypno porn, with a strong, frequent incidence of furry porn along the way also.

There's some overlap but that's pretty much the whole story.