On a lot of those shows, the overweight contestant is closely monitored by doctors and medics during the entire time. It is extreme and I think it serves twp purposes:
1. It pushes them past where they never thought they could go to show them how tough they are and how much tougher they will need to be.
2. It gets a quick scale reduction result, which is likely to reinforce motivation.
I agree that it look INSANE.
"Look son, there comes a time in every man's life when he has to make a decision. Do you want to be big, powerful, jacked, yoked-up, have women everywhere want you and men fear you . . . or do you want to do crossfit?"