Possibly because you can completely avoid alcohol but you can't completely avoid food. Some large percentage of people who would have been addicted to other substances (due to less than optimal nature/nurture) but didn't, because they did not take those substances, instead became addicted to the substance of food.

It might be more useful to see addicts to every type of substance as a large pool of anxious people who came across a substance to self-soothe, and figure out how to address the anxiety problem first.

Cheaper, much easier to get, socially acceptable everywhere, ...

You won't get judged for eating alone at home, but start drinking alone at home...

The US population probably isn't much different from the rest of the world, in that regard. What's different about them is they live in the US. Drop foreigners from skinnier countries in the US, and, as a cohort, they'll gain plenty of weight (as with lifelong Americans, some individuals will buck the trend, of course)

It's a complex social-environmental, economic, and political problem.

Part of any process is the ability to follow it. If you tell me you can drive blind folded by just memorizing the streets and driving precisely -- does that mean the process really works if no one can do it?

It's normal not to call that an effective intervention when only a small minority of the population can pull it off.

Things that do work ultimately do so by that mechanism (of course!) but not via people trying to eat better and exercise more per se. They do it by changing the circumstances under which a person is making decisions about eating and living, so better eating and more exercise in-fact happen, consistently and enduringly.

From most- to least-effective, over the long haul, it looks something like this:

1) GLP-1 agonists & friends,

2) Move to a skinnier country,

[a large gap]

3) Months and months, probably with periodic long refresher-sessions every year or two if you want it to actually last, of high-touch expensive help from multiple specialists, amounting to hours per week. This is the gold standard for what "actually works" as far as what can be done as an intervention, before Ozempic and such, and its outcomes are... so-so.

[another large gap]

4) Basically any diet & exercise plans or attempts to simply "eat less and move more"

(throw gastric bypass and stuff like that in there somewhere, not quite sure where they fall)