There are several other forums I visit where people are have commented on activity fading over time. To an extent I think that over the past 15 years since the Internet began to really take off people have had tons of things to discuss, and now, the novelty of forum discussion has somewhat worn off and everyone feels like they said what they wanted to say (along with burnout from endless debating). Such trends do vary though, new forums that address old topics in a new way generally get a surge of activity for a 2-3 year period.