I think it's less about becoming the opposite sex and more about just trying to escape from yourself. To be a troon is to attempt live in a constant state of dissociation, whether the fantasy of one's new self is fueled by cooming or yaoi plotlines or just being a new and different person as a man/woman.
It's not a coincidence troonism started getting so big right after technological and societal developments (high-speed internet, easy access to porn, streaming, social media, smart phones) made it possible to spend most of your waking hours in a numb dissociated state where you can kid yourself that you are a different person, or at least not really present in your own reality.