I realize the vast majority aren't, but I'm curious if any are and what their reasons are (i.e. a cisgender man who decides to be a woman).
You see widespread homosexual behaviour (and real deviant sexual behaviour too, like pedophilia and beastiality) in societies which limit the access between genders. It's possible to imagine some heterosexual people adopt a homosexual lifestyle thanks to lack of access to the other sex, but it's hard to imagine it becoming a identity in USA outside some imprisoned individuals.