Probably because the parents are whales themselves and are too busy shoveling cookies down their own throats.
Parents set the example - most kids with horrible eating habits usually pick them up from their parents. It's up to the parents to set the example by not having that crap in the house in the first place.
I think another issue to keep in mind is the prevailing attitude toward "fat acceptance" and the general shirking of responsibility that is coming from Fat America these days - everything from "genetics" to "stress" to "evil corporations making me eat this stuff" that in essence reinforces the message to parents that it's OK for the kids to be a "little overweight" -
Many parents also seem to have the attitude that it's OK to let the kids enjoy their 'treats' - that it's OK if they're a little fat, it won't be too bad because they figure they can always lose the weight when they become adults. The reality of course, is that most people will never lose that weight - and voila - we now live in a nation of porkers.
but I applaud the concept of the show - at least they are red flagging the issue - I'm curious to see how they deal with it.