Biggest factor I think that made the discussions better is that folks were not connected all the time so discussions would span days or weeks. You had time think between posts. Folks would log on once or twice a day. Obviously there were exceptions. Today a reddit thread has about a 24 hour shelf life because of its global nature, and then it dies. Furthermore the most intense discussions will happen in bursts and then flame out. People aren't engaging in discussion they are shouting their opinion into the ether and moving on.
Second factor obviously is the tremendously larger and more diverse population on the internet. More people mean more new topics posted and less time to discuss topics. The actors are less technical overall than those who had internet in the 90s and early 00s.