[Kirby64]

It’s a combination of societal weakness/acceptance, marketing, and access to easier alternatives (eg, stuff that will make you fat) in my view. There’s not one thing that does it, but years and years of… conditioning that’s led us to this point.

[amanaplanacanal]

That's certainly one theory. Among many. Science is about designing experiments to show which theories are wrong, and which are correct.

[Kirby64]

Right, and science shows that in calorie controlled diets (where people have their diets carefully controlled), they have no issue with weight loss/gain/whatever.

This leads to the obvious conclusion it's peoples inability to manage how much they eat that leads to their obesity. What else could it be?

Granted, this isn't necessarily their own moral failing... but the environment they're put in does not set them up for success.

[amanaplanacanal]

Sure, it has to be environmental, since it has affected millions of people (and animals). The question is: which environmental change? Ultra palatable food? Ultra processed food? The demonization of fat and subsequent additional sugar? Plasticisors in the environment? Lithium in the water supply? Something else?