The forum has been left-leaning for a while, but at the same time I see the demographic shift as a reflection of the polarization of the right.
Trump has served as a wedge in conservatism: he pushed some people away from mindless support of right-wing ideology, and others deeper into it. So it looks like there are fewer conservatives overall, but the ones who are conspicuously conservative are often (not always) rabidly so -- to the point where they support dogwhistle racism and xenophobia.
I wouldn't be surprised if a few conservatives got themselves banned, since the more extreme examples sounded like they were about five minutes away from committing crimes.
I think that's part of it.
I do think that some have started to see how toxic the modern conservative ideology really is. Its basically casting off any pretense of actually caring about people, and has become openly antagonistic towards the People. I think a lot of that though is just the mounting evidence. Some of it is historic (and actually isn't a Republican issue, the US has many failures that transcends party politics, the thing is, one group is far more willing to admit and want to work towards solutions of those issues, the other wants to act like they somehow simultaneously didn't even happen, but weren't problems at all but would be great to implement even more strictly). But the past couple of years has made it impossible to ignore how openly hateful conservativism has become. Its kinda like with topics like sexual harassment and assault, where people had blinders on, but then it was like suddenly people are going "whoa, holy shit, this is a serious problem". I don't think its a coincidence that people seeing how toxic the rhetoric that conservatives are spewing is happening at the same time as people wake up to some other serious problems. People have been knocked out of their stupor, and its sobering.
Quite a few of the "missing conservatives" on here though are just chickenshits that got tired of people calling them out for their bullshit and so have been out seeking "safe spaces" where people would just parrot their, often outright wrong basic facts (let alone when discussing topics with lots of depth, like Middle East relations) instead of, you know, reading even the articles they themselves were using to support their idiocy and going "you know the article actually doesn't even support your opinion?" type of stuff. Like rudeguy (I recall him going in OT and losing his mind over Obama taking selfies with some other world leaders at a celebration event after Mandela's funeral, because he couldn't accept that it was for celebrating Mandela, and not a somber event with Obama being so disrespectful). And that's before you get to the morons that just push completely nutter-butter conspiracy garbage where there's been a pushback against that.