There definitely should have been a 'test-case' along the lines of a sample of people who have made permanent lifestyle changes, e.g. commuting to work by bike/foot, doing physical activity every day, rather than 'fad' exercises.
My own slimming plan: Cycle 200 miles a week and eat carbs like they're going out of fashion.
This is my point about intrinsic motivation - how many people who run every day, cycle every day, play sport to a serious level or whatever can there be who purely do it because they feel they should lose weight, or because their doctor tells them too. They do it because they enjoy doing it and like feeling fit and looking good.
The problem is that monetising and really convincing people to 'go for a run because it is fun' is much harder than 'come to the gym because you're fat', even if the second has a very low long term success rate. The low long term success rate being part of the business model for gym based exercise anyway - their dream customer is someone who pays a subscription, then stops coming whilst still paying. It isn't in their interests to turn everyone into regular athletes.