Because they are insane, or insanely stupid, or both.. At my gym there is a older guy who do pelvis thrusts with a half a ton. He look like a unemployed janitor, but he is very proud of himself, when he do one rep max with the 1" range of motion. These guys have no comprehension what so ever about how they and their lifts looks like at the other people's view. When they look at the mirror, they see some kind of super athlete, while others see only some ridiculous moron struggling with the overload. Why do you think that moron is lifting in his parents basement instead of real gym? He is a village idiot of some sort.. 
Not really. His wife and daughter are living upstairs. And one certainly couldn't do these kind of lifts at or bring this intensity to a commercial gym.
He had an interview with WWE recently.
