The answer is because the judges don't have the balls to mark down stupid physiques. And as long as the judges do so, bodybuilders will keep trying to look stupid in order to win.
Bodybuilding is essentially about 'awesome' because the mentality of teenagers is focused only on what is easily visible. In bodybuilding, that means size and conditioning. It takes sense to understand what quality is and teenagers rarely have the attention span for it.
If the judges really were professional and bodybuilding was treated as a sport and not as simply a spectacle, the concepts of aesthetics, proportion, balance and presentation would have long ago been ingrained into the bodybuilding public.
Unfortunately, this never happened.