Some people just enjoy sex and once they have crossed the biological gender line, maybe through same sex experimentation at school, they are open to doing it with anyone they find attractive.
We've all had drunken fumblings with the same sex after a club night when we've had to share a bed. I think experimental just comes from human curiosity... sorry, I meant when younger, as I am 58 now!
The writer Anais Nin, who wrote a great deal of erotica, actively explored her sexuality, developed an attraction to her lover (she was already married) Henry Miller's wife June (see the film, Henry & June). Ultimately, she came to the conclusion that she didn't like the physical side as she didn't like the taste of vagina. So people form their own conclusions.
According to my gay friends, very few straight men will turn down the opportunity to have their cocks sucked, which is why there is often 'activity' in men's toilets. In the post war years, the police used to catch homosexuals there.
We mustn't forget the the hippies, and the Summer of Love (1967) where sexual experimentation was at it's height. People were basically getting off their tits in more ways than one.
I think today we live in a more neo-puritanical society (like the Victorians). I have no idea how sexually active Gen Z are, as I remember reading somewhere that they liked to be in bed by 10pm and didn't drink or go out much...