I think that there are a lot of layers to homosexuality. I think some truly do have the wiring to be gay, that is not up for dispute here of course.

What is most common is the grooming, from all facets and vectors of attack. Maybe shows spend extra time normalizing homosexuality (because of course, the characters in these shows can never JUST be gay, you have to go through their life's story and watch as they run their entire life's identity as being gay), or maybe the media or big tech or government push it. Maybe they spend enough time outlawing discussion or criticism which causes cultural shifts and a focus on how cool and unique you are (and how untouchable you are) for being gay.

All of these things happen. I don't know about a parasite in the way you mean, but children are infected by parasites from day one of their life nowadays.