Didn't Bob say last season (or maybe it was this one) that one of the past winners gained all of the weight back?
The original biggest loser from the first season has gained back all his weight.
Please remember that food is a HUGE addiction to these people. So they are going to yo-yo just like the rest of us "normal" people who aren't on television. It's easy for us to say they wasted their time and someone who really wanted this should have gotten a shot. These people, at the time of their casting wanted just as bad. There are other factors...
You're only committed for the duration of the show. Your spouse isn't supportive and you get tired of making 2 different meals every night. Something horrible happens which drives you back to eating.
It wasn't until a few seasons ago where they even mentioned that they tried psychological healing. Actually, it's still not totally done b/c the support is "said to be there" but in the end they have to do what their trainers tell them. I think last season was like the first season where they had access to a gym and trainers once they left the show.
So the show, behind the scenes, has evolved some...but it's still a show and it's still all about doing the most for as little money as possible.
Ali has been able to keep the weight off. That guy before her (the twins) have been doing well. Mark has gone back and forth. Suzi was doing really well until she got pregnant and then she got pregnant again. Matt, of course, gained some with her.
But few that lost over 100 lbs have gained all that back. Some have gained 40 - 60 lbs back but perhaps they didn't want to be a size 2. That is hard to maintain for someone who struggles with weight.