Personally I think the increase in LGBTQ people would most likely be caused by increasing public acceptance and/or awareness - if you're going to be ostracized

Personally I think the increase in LGBTQ people would most likely be caused by increasing public acceptance and/or awareness - if you're going to be ostracized by everyone you know it's a lot harder to come out, and if you think feeling however you do is bizarre/unprecedented/obscene you similarly won't tell people. Plenty of anecdotes out there of people who didn't think they were gay/bi/trans/etc because they didn't think of it as a thing-you-could-be; you see things like "oh, I thought everyone thought girls were hot" (or equivalent). As acceptance and awareness grow, the bar gets lower -- fifty years ago it'd take a lot of dysphoria to justify trying to transition; now it's still not simple but it's a lot easier, and so more people who are comparatively less dysphoric are willing to take that particular plunge, and more of them know it's a doable thing.