Physical fitness of contestants

I am not here to body shame anyone, but why would you go on a physically challenging show not be in good physical shape?. It just boggles my mind , why you would go onto a show knowing that it requires significant physical ability and not train for it? I run in endurance like races and obstacle course races and train for months before the race to ensure that I'm not going to get hurt and I'm going to finish and that I'm not going to hurt anybody else on the course. I don't get it.