Oh why do you think there hasn't been a successful karate practicioners in ANY combat sport? Lets see here

Lets say match 1 is pure striking stand up
Karate Kid would get beat by a boxer or kick boxer by pure out striking
Karate Kid would get kneed to death by a muay thai fighter while grappled
Karate Kid would get elbowd to death in a grapple in the coner
Lets say match 2 is pure ground game
Karate Kid would get ground and pounded till he was knocked out
Karate Kid would get submitted not only on the ground, but standing
Karate Kid would get tossed around by a wrestler till he got the postion he liked
Lets say match 3 is MMA rules
Karate Kid may be getting the better stand up of someone, but then he gets takin down, what does he do? I know he doesn't know cause he hasn't learned ground defense
Karate Kid fights A,B or even C ranked striker and Im putting my money on the MMA strike over him anyday. Why? Karate Kid would be using kicks and punches, while the MMA striker would be using kicks,punchs,elbows,knees,grappling,foot stomps,take downs,submission attempts ground and standing

Lets face is karate has yet to make a impact in ANY combat sport, and I doubt it will.