Moreover, a lot of the exercises they use on the show are of little benefit and physically unwise for unfit people. Flopping the big tire, dragging weights, and doing all that TV boot camp crap is less beneficial than a simple bike ride. God gave us bicycles so we wouldn't hurt our joints while losing weight. But I guess that bicycling is boring to watch on TV, so they get them to do stupid, wasteful, and stressful stuff.
The exception of course is some activity which shows accomplishment. Chin ups are worthless for weight loss, but if no one has ever done a chin up, to be able to do one might be motivational. No one dreams of the day when he can flop the tractor tire.