Forums were far superior to modern social media, combining the best aspects of BBSes, IRC and the web, but were not corporate-friendly and not easily-monetizable. Which is why they had to go. Forums were intolerable to MBA types who “needed” stats, homogeneity, and the ability to control discussions. Related to that, they were also not propaganda-friendly.
I’m not surprised forums were killed off; I’m more surprised they lasted as long as they did. From 1995-2005 or so, you could find a vibrant, interesting forum for anything you wanted. Now they’re almost all defunct and the ones that persist do so in a much-reduced state.