Actually, there is a lot about this that helps to solve the problems that are contributing to American obesity. This can be done at home, at people's convenience, and can be flexible enough to help build habits.
Sure, it's not as easy, or as worthless, as pontificating that others should do better than they do, but a home program is easier to start up again when it has slipped, doesn't involve going somewhere else and all that is involved with a gym, and doesn't involve expensive and difficult to cancel subscriptions.
Moving more, which is what these classes are about, burns calories, helps raise metabolism so that more calories are burned when not exercising, and can contribute to lowering tensions, which tend to lead to eating the wrong foods.
Yes, people in the US, on average, tend to eat more carbs and sugars than they should. A lot of that is because the food industry, with government assistance, has done a great job of hiding those things so that it is difficult to avoid them. This provides one step for people who want to take care of themselves to do so while still having some fun and relaxation in their lives.