None. It's literally as simple as doing what you already know you should be doing. Why is this so complicated to understand?
so what is the reason why so many people are getting obese in the USA? Is this some moral (or other) weakness?
Discovering the correct reason(s) why for a situation enable the use of effective solutions for a problem.
This includes multiple contributing factors to any situation.
Attacking the wrong problem will lead to ineffective solutions.
Obesity is a complex problem with many contributing factors.
YES doing the right thing is important. But ignoring and not correctly identifying the contributing factors can hobble efforts to solve the situation.
Asserting that there are no relevant contributing factors is willful blindness.
It's not a weakness. It's lack of care.
Literally everyone knows that you don't actually have to eat more than you need to survive. You can't get out of elementary school without knowing this. Calories in > calories out = weight gain. It's basic knowledge every citizen knows.
They just don't care.
I promise you that if there were a magical disease with an accurate diagnosis of "If you're still obese in X months, you absolutely will die" and the literally the only cure was to lose that weight, that pretty much everyone would stop stuffing their faceholes. Overnight.
It is not more complicated than that. They just don't care. Anything else is a complication.
Everything else is a story to make people feel better.
Literally everyone knows that you don't actually have to eat more than you need to survive. You can't get out of elementary school without knowing this. Calories in > calories out = weight gain. It's basic knowledge every citizen knows.
You presume better results from education than might be warranted.
A lot of people do not make that simply logical connection between the facts you mention and their own health and mortality. They know it all, but do not do the math.
None. It's literally as simple as doing what you already know you should be doing. Why is this so complicated to understand?
Edit: will power fails because it implies that there's temptation. Temptation exists when you decide you want something you shouldn't. Just decide you don't want it. It is indeed the root of that.