I don't know why it's got that reputation really. It's probably due to people who've never watched it hearing that it's no holds barred fighting (which it isn't, and hasn't been since the early 90s) and assuming that that's what it will consist of. Even when there weren't really any rules though, the disciplined martial artists were still the most successful combatants. Now, there isn't a choice as technique, fitness and skill have to be ridiculously good for someone to even have a chance at making it.