It's simple, it's not easy.

> other people are eating less and losing weight. No, they're not, and that's my point.

Look at smoking that you mention. Smoking was unbelievably common a few decades ago. It's now pretty uncommon (in North America). Why? Were people just failing in the past, and now aren't failing? No, we made public health decisions that have dramatically dropped the proportion of the population that smokes cigarettes.

IOW: Treating it as an individual failing may feel good, and may even be "true", but it's not a useful framing of the problem. Treating it like a public health issue is massively more likely to work than just wagging your finger at people and telling them to just eat less.