Critical Mass.

Usually there is a group of very enthusiastic and competitive individuals that promote the class and help build the fleet through a lot of different activities (volume discounts, fleet trailers, etc.). Everything has to come together for the class to establish a foothold; the boats need to be solid, the competition needs to be good, and things need to be affordable within a certain range. Once all this is done, the fleet has to hit a critical mass before it will self propagate. F18 has done that most recently and if you look at the F18HT I think you'll see a fleet that, among a few other issues, never quite reached critical mass and it quickly died.