I think it's just the rate at which new posters land and old ones leave for the real world. This goes for any board, really. I know that when I was on the frequency of a societal being, I had absolutely no motivation to come to places like these. That could be one possibility.
Ever since the expansion and change in general atmosphere of *chan culture, I've felt less and less like home on online. I feel like the state of the internet is going to force me off the internet into the real world, as weird as that sounds.
Also, just a reminder to everyone to let go and not be afraid to post your ideas. It's easy to tell that lots of you lurk but never say anything. You can see how quickly posts pile up when someone makes a new thread compared to when nobody says anything for days.