I think it might have something to do with changing social standards. There is always a group of people who are afraid of any kind of change - in particular, change that makes them feel like their rights are being taken away. For example, the right to pick on a minority. (I'm not saying that it ever actually way "their right" btw; it's just that I think that they perceived it as such.) It used to be a lot easier to pick on minorities, like the LGBT+ community, and find resonance with other people. Nowadays however, there's a good chance something like a sexist joke will hit a brick wall (which, imo, is a good thing). The feeling of social exclusion is one of the most terrifying feeling a human can have, which means that your mind will seek for any way to "address" this issue. But of course, you don't look at yourself (You where able to do it in the past, so why shouldn't you be able now?), you look for some external reason for your problems. And the "obvious" target in this case is, the LGBT+ community.

Note: This is just my own interpretation, the interpretation of a straight male bystander, so it might be entirely wrong. In addition, I don't believe this is the whole picture, or even anywhere close to it. "Hate" is an incredibly complicated and nuanced topic, and there's no way I could get it fully right.