Unlike social media, few of these forums have mechanisms to "like" or upvote posts so there is no reward for posting just to attract attention, whether it be positive or negative.

Those types of forums are great, but just as a counterpoint, I get a lot of that type of value from Facebook Groups as well. There are niche specialty interest groups with people of different skill depths conversing on probably just about anything.

It's mixed in with the rest of your Facebook feed most of the time so it is a categorically different experience/"community" than an independent forum but I don't think the "like" mechanics materially affect the discussion in those places.