I am over 50 so have watched America get fat - when I was in grade school we had one fat girl , Tanya. I’m sure she had some metabolic issue, and I’ve since met a few other people like that, athletic but obese.

My kids go to school with so many fat kids that they don’t even notice it.

It’s more complicated than willpower, systems here are set up to almost enforce inactivity, and obesity is epigenetic, if you are born to a skinny mom but get fat, a genetic switch flips and your children (even if you don’t raise them in an obese household - for example you die and they grow up with skinny grandma) are very likely to struggle with obesity.

But it’s also true that you, as an individual, have the biggest impact on your body size. It’s just not true that everyone’s appetite and metabolism are the same. I come from a thin mom who herself had thin parents, and I’m taller than average, my body is easy to keep slender even now.

And I’d describe the problem as habits not willpower, nobody has enough willpower to fight an appetite for a lifetime. Habits are what matter, and in places where there are many obese people, they sort of distort society, making it more difficult to be active (car centric cities, elevators for everyone, desk jobs).