That's because HE had a serious mental disorder. "Gender reassignment" surgery can't fix those. And neither can publicly "self-identifying" with the opposite sex.
At some point down the line, I expect ‘intelligence reassignment’ to occur....where you can select ‘stupid’ or ‘dimwit’ and do this for six months, and maybe upgrade to ‘clever’ or ‘Einstein-like’.
This happens all the time, because as you say it is a mental not a physical problem. Once he got fat and ugly and was no longer the object of affection from other perverts and couldn't get attention from unsuspecting male victims he realized it wasn't a fun game to play anymore.
One of my best friends was given custody of his two kids after his wife divorced him when things with her boyfriend got serious. His ex-wife had a history of problems with alcohol and emotional difficulties. His daughter who was kind of a tom boy was always very close to him. But when she turned 13; she had some problems with boys and other girls being mean to her at school. She wasn't happy and decided that she would have preferred it if she were a boy. With all this "transgender" crap going on she quickly found out that pretending like she was a boy got her a lot of attention from everyone. The ex-wife saw it as her ticket to getting the kids back. She took her to some quack lesbian counselor who had no legitimate credentials, and things just went down hill from there.
His daughter wanted to change schools and was introduced at her new school as a transgender boy and all the kids were advised not to pick on her. It seems like that would be a disaster, but because of all the media coverage of this type of thing... she became an instant celebrity which was further motivation to continue her new identity. My friend took her to an actual mental health professional and the guy identified all of the motivations that encourage his daughter to continue this perverse fantasy.
My friend has been repeatedly condemned for trying to interject any common sense into this bizarre situation. And his ex-wife has used it to manipulate her daughter into moving back with her. It is all very heart breaking.