> 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.

I’m not convinced. 4chan doesn’t have any of these mechanisms, so the proxy just becomes the number of replies you receive. The chief benefit of forums is that they are smaller. This is good if the original base of users is good, and untenable if they are bad—and they usually are bad. I always hated forums when I was younger and was glad when Reddit killed them. Of course, Reddit brought its own problems, but even in the state it is in today I find it infinitely preferable to forums.