Both appeal to the same fan base, when the bodybuilder begins training BJJ, Muay Thai, wrestling, etc, they find that years of heavy lifting has built non functional muscle that looks good and last 30 seconds, then the former BB gets into crossfit, kettlebells, functional strength training, loses 45 lbs of muscle and gets called a geek with 13" arms, but he can kick the bigger, gym stronger, more intimidating dudes ass, so he doesn't care. Not to mention the top MMA fighters make 10X what the top BBers make anyway, so who cares?