In part, I think, because the OT thread has a lot of cross-game comparisons and general fun, but also because so many members of the main thread have been banned (some for seriously stupid-ass reasons - though my ban was fairly earned, I was a dick) so they can only participate in the OT thread. It's a more relaxed environment.
On the positive side, when the update does finally come out, it isn't going to be the OT thread spammed by 600 morons asking why their game is crashing (because they used mods) or where to download the latest version (which is always in the goddamn first post), so it may prove to be quite relaxing as this place goes from 10 or so posts a day to several thousand (like it did with episode 8).