i think that events like the release of a new album or so bring more people to a forum and these people will then also take part in other discussions. but after these "events" are over it all calms down again.

and here there were many many discussions in the TLFR forum after the release. now there isn't as much "new bon jovi stuff" to discuss for a while and people won't even come here and see that there are still lots of interresting topics in the other forums.