And as mentioned - endurance is a useful attribute. If they can make additional money working both sides of the fence, so to speak (I was going to say “both sides of the street,”, but…) then perhaps some have a preference or reluctance, but I wonder how many stand on principle? Plus, I’m not conversant with the size distribution in real versus movies, but I gather than having extraordinary endowment would also make an actor in high demand going either way.
I’m going to guess, based solely on what I read about the sordid life of young gay male prostitutes that many do it because it’s a living, and actual orientation does not figure into it as long as they can make a living, so whatever category they get started in pays the bills.