Genetic differences can exist and not be meaningful if the situation doesn't allow for them to be meaningfully expressed.

We know that people just have different metabolisms, different levels of hunger response, different levels of "food noise," etc.

We see obesity rates raising in nearly every country across the world as economic power and access to ultra-palatable hyper-calorie dense food increases. This is universal across the developed world with very few exemptions - Japan seems to largely be immune, but Korea and other portions of Asia aren't.

The growth curves look very similar, despite many of these cultures across the world putting even more emphasis on discipline and responsibility than America, things that in theory directly align with being more responsible about diet. If genetics weren't involved and it was all willpower (and where does the capacity for willpower come from? Is there no genetic component to it?) we wouldn't see these growth trends be so similar to America and each other.

I am not sure the genetic angle but there definitely is something happening at a craving level in the way the mind is responding.

On the flip side I don’t think your comment holds much weight either. A large portion of the population worked trade jobs and the access junk food was a lot less prevalent. You kind of have a good recipe for unhealthy population now. Low quality foods and less activity.

Because genetics alone aren't enough, you also have to have opportunity.

If you don't have enough food, no one is going to be fat. If you have plenty of food availability, then certain people are going to have genetics that make it more likely they end up fat.

Not remotely weird: people were poorer and food was more scarce across the board pre-WWII.

Many people pre ww2 were perpetually hungry. Now they can afford as much food as they want

Or that it happens overwhelmingly in specific places with a very broad genetic mix.