I think it's more a case of the long tail. There are a few things a lot of people are interested in, and a lot of things few people are interested in. It's probable (IMO) that most people are interested in things that aren't the few big things, but everyone is interested in different things, so it's hard to put together a game.
I wonder if anyone has ever considered putting together a small fandom game, i.e. like a multi-fandom game, but only small fandoms allowed.