That doesn't necessarily have much to do with how damaged his brain has gotten. In fact, it has let him take more punishment. The man has had more than eighty pro fights.
When I said stopped I meant stopped by the fighter, not the ref, I should have said KO'd. When you get knocked out it is the huge impact on the brain that forces it to shut off. There is no more "punishment" that can be taken. More punishment than that would induce a coma or even cause instant death.