fighting games are basically cartels: you have a couple strong sets of IP, outside of which it's insanely hard to get traction - uber small community to start with and new titles often need bootstrapping and refining [no tournaments/scenes/bad or no online experience, etc.])

it also works backwards: since everyone moves to the latest and greatest, the community evaporates when a new version comes out: nobody still plays street fighter (version - 1) basically as soon as the latest comes out, as tournaments pick it up (=> you need to learn it)

the one dark horse was smash, which had insane longevity but nintendo didn't want that IP associated with the fighting game community/streams for a long while - not sure what current state is