I personally don't believe they have. I didn't make the decision to be "straight". I was just born this way. I don't believe anyone makes a "decision" to be straight or gay. It has to do with genetics or hormones or DNA or chromosomes or whatever. But it's certainly not a decision. Did you "decide" to be straight?
Cart before the horse. The overwhelming percentage of the world is heterosexual. All creatures reproduce through heterosexual mating.
This is the "standard". Homosexual is a "deviance" away from the norm.
No one choose to be "straight". It comes by birth.
Language and cultural identity/behavior come from environment. Crossdressers aren't genetic (we are born naked), can we agree on this?
Homosexuals are also influenced by outside elements (it is not genetic).