I understand your basic point, and I don't fundamentally disagree with it. However, I do think it's a lot more complex than that. There are those of us who have had many things "go wrong" in life, thus making the decisions to exercise a lot lower priority. For example, if someone can't pay the rent, or they have a brother who just committed suicide, or a son who's drug addicted, or they've been sexually assaulted, those major life events can take precedence over "eating well" or exercising regularly.
As someone who has had multiple traumas in the last decade, I know my weight gains (and sedentary lifestyle and shit diet) are my responsibility and my choices. I also know I'm an extremely high-functioning person who has survived a lot of things, other people might not have. Exercise and diet just aren't that high a priority given my life events.
Just Google Dana Rivers, Oakland, and you'll get it.