Probably because of all the kung fu guys butts he's kicked over the years
I understand that their attitudes sometimes rub people the wrong way, but even if you dislike him for that you got to respect him for what he's done. He stepped up and proved that martial arts could do what everyone had been claiming but no one else could do.
That a small, not particullarly strong person could beat a much larger, stronger, more athletic and very tough opponent. Royce's dominance in the UFC changed the ways people view fighting, before that ground work was basically ignored flat out.