[Koko Ed]

I think one of the main reasons the original seven(?) have survived so long is solid sponsorship.
What also helps is proximity to competiton. It is easiest to see an explosion of rookie teams where there are local regionals (such as Finger Lakes this year) because they don't have to play for traveling or lodging and such. Just the competition. Teams off the mainland are in dire straits and unless there is significant industry around or government support they really struggle to get by.