You know, I didn't see this Thread. I think I'll add my story.
I've been a lurker and then member of SB for more than 20 years. Much of that time, it was just a geeky hangout, with fanfic being the main part. Political elements happened, in and out of stories, but it generally wasn't that big a deal.
Over time, as others have pointed out, things got more pushy. The things that really killed me, the final straw was when "Trap" became a slur, because I've run into people online who called themselves traps, and weren't shy about it. I though they were screwed in the head, but if they wanted to call themselves that, I couldn't see the problem.
I was infracted over that one. It was the last straw for me. Before that, there was a Thread talking about Trump, a more reasonable Lefty wanted to know why people could possibly like him, and while I wasn't infracted there, I did find that it was pretty much just me being reasonable, while more, and more, and more people tried to smash me down as I put up moderate, reserched views about why Trump could be seen as better than Hillary. I gave up, after a while. There was more, stories I liked being booted of the site, some coming here, some not. There were people getting banned over pretty close to nothing. There were Mod Vs Mod arguments, and it all pissed me off, so now I pretty much only go there for fanfic. I wasn't particualy happy with it being sold and monetised, but it'll slowly die, so, that's just how it goes.
Over all, It just changed from a relaxed site, where you could chat in peace, to something much more restrictive, and I gave up on it as a result.