@cp2000 I hope what I write here isn't a "therapy session," as @ianfontinell-0 puts it...
Thank you for sending the links to the torrents. I downloaded some of the material, and it's pleasant to view. But to the greater point of "straight" guys having "gay" sex, and enjoying it, we need to make some distinctions. (Note, though, that the guy on the torrent page was never seen to engage in any gay sex, even if he showed his hole.)
Categories like "straight," "bi," or "gay" are difficult to define, but they're about who people are attracted to, who they form deepest relationships with, etc. It's something of the mind.
Actions like "gay sex, [and let's assume that it's two men] are just that--activities. They don't necessarily reflect someone's orientation. Many of the models/actors whose films appear on this site are in fact straight guys, some married with kids, but they can enjoy a good blowjob, fucking a tight, slippery hole, or having a prostate orgasm. They especially enjoy being paid for doing this stuff. It doesn't mean that they're gay.
You mention the possibility of generational differences: I think you're asking if "straight guys having sex with another man" is limited to "millennials." I don't know of any studies on this, but I think the answer is no. Rather, I think guys who want to experiment or play are more likely to do so within their own generation, as that's who they can best relate to, and they probably have most of their friends in their same generation.
Thanks for raising an interesting topic.