Who knows why? It could be any number of reasons, like I said. It could be as simple as someone wanting to experiment or they are curious. If doctors/scientists who have studied people don't know, then how should any of us know? I'm sure it's a real thing for some people (who are ONLY attracted to the same sex), and not the real thing (but something done for various other reasons) as I noted above.

I'm sure I've heard of people who thought they were gay when they were younger and went straight when they got older, so maybe they were confused about their sexuality for whatever reasons. I don't know how much a liberated society plays a role in someone's sexual experimentation or sex life though, as in what they would be willing to do. IOW, if you are sure of your sexuality, you aren't going to be needing to experiment with the other no matter what a society says is acceptable.