Society in recent times has attached so much honor to victimhood and oppression and the only way for a straight white male to receive some of that attention without joyously putting dicks in their mouth is to pretend that they are a woman. If you get the right kind of attention seeker and they happen to be a woman, black, gay, whatever, they'll cling to that identity and proudly wear their "victim" badge. If said attention seeker happens to be a straight white male, they will get incredibly jealous of the free attention the "oppressed" groups get, so they'll decide they are a lesbian now, that way they can still be a straight white male, but also get LGBT oppression points. Women already get oppression points which is why FtM trannies are so rare. And statistically speaking, the more of a certain group there is, the higher chance of some of them being completely batshit crazy.
TL;DR: Insecure male narcissists wanting to be extra special. Most female narcissists already feel they are special because vagina.