If there were respective pro leagues (wouldn't happen in america but maybe across the globe in some places) for the various fighting styles, i'm sure the champs that are now in mma would head to them (if the pay was comparable). The problem with that is that theres so many different fighting styles (some of which are not suitable for actual combat: kung fu and karate aren't feasible, the jury's still out on tae qwon do as i haven't seen enough of it yet to pass judgement) you'd need atleast 10 different leagues for them all and by that point your pool of participants would be greatly diminished. Even now there's probably more ranked fighters in the heavyweight division for boxing than there are total combatants in the UFC and K-1 combined.