Web forum software bumps up a thread to the top of the board when a user posts a reply to the thread. This enables lengthy long-lived debates to take place. It gives a lot more opportunity for good ideas to be presented on a topic compared to reddit or lemmy which cycles posts off the front page hours or days after being posted. But trolls can easily derail the entire purpose of the forum by insisting on always having the last word in an off-topic, manufactured debate that eventually draws the entire userbase in.