So you're saying that maneuver a 200 pound dumbbell = maneuver a 200 pound person?
A dumbbell is in the form and shape do be easily maneuver. try to do the same with someone that weights 200 pounds.
And plus a how long a bb can hold 100% of its strength? 30 seconds to a minute.
Welcome to the top of the food chain. 
Well, do BB:r need 100% of his strengt to bitchslap some teen twat senseless, while it means slapping twat's head of the body? He needs at most 15% of his strenght, everything more than that is showing off and can be dangerous. Don't forget that we are talking fight between Ronnie in his prime vs. delusional getbigger twat, not fight between Ronnie and Cain Velasquez.. Can you understand? You shouldn't fight with the guy who is capable to lift you with one arm with no trouble at all

So, why these guys don't go for it, and take over MMA scene with no trouble at all? First of all, it isn't their sport. No interest what so ever. Secondly, they get their fair share of injuries by lifting weights, and really doesn't need more. But how about top boxers and MMA fighters? What they do to boost their ability to fight better? They use gear and lift weights. You see more bitch tits in boxing and fightsports than bodybuilding, and they all lift weights to get more strenght and bodyweight.