There were always plenty of forums full of people with only a passing or casual interest. Even outright enormous lunatics - it's just that it always seemed a bit more reasonable overall: Everyone cooperated to not let the place go to shit immediately and the need for huge and unilateral moderator intervention was limited.

I think the large social networks have mostly poisoned a lot of people with harmful memes (the need to shout, weird conspiracy theories, etc) and now that the damage is done it's too late even for the old format. As a society we've moved past being adults online and degenerated straight into childlike behaviour.