I've started threads that got only one response, and one that's closing in on 2,000. Makes sense to me, without a doctoral thesis. Threads that are very specific don't last long... lyric requests, for example. Once 26 variations with complete discographies are posted, there's not much else to say. Threads that are of borderline interest to the community (Jazz and rock and roll in the music section) die a rather quick, but dignified death because there aren't enough people to keep it going. Threads that are more open-ended, or encourage witty reparte are the ones that last the longest.
And of course, the political ones. But, even the political threads are relatively short-lived if they are about specific politicians or issues. There's always another goblin lurking in the bushes, ready to be vilified. Threads about Republicans have a much longer shelf life than ones about Democrats...

Jerry