My father in law was an over the road trucker for 20 years, he was in the armed forces before that. 20 years of long hours of sitting in a truck with little exercise and easy access to junk food and he is now elderly and a "land whale", he is barely able to move. Again, he used to be military-fit.

He eats right now that he's retired, he keeps a calorie diary and he exercises as much as he can (which consists of getting up and walking the length of the house and back to his bed until he is exhausted.) He lost about 100 pounds but it stopped there due to his age and inability to do harder exercise. He has nurses who check on him in-house bimonthly and dietitians who watch out for his eating habits in relation to his heart but that 100 pounds? That's all that seems to be coming off.

It was so easy for him to slip into a bad eating habit due to the only job that was really available to him after he left the military and the sheer availability of absolutely unhealthy food on the roads in America. Sure, he could have not eaten so much but my point is it was incredibly easy to eat poorly and much harder to eat well on the roads in America.

It's not always "100% enabled by assholes surrounding them."

In all cases is it literally a matter of energy in vs. energy out? Yes. But we have a problem in America (Britain as well) that is more systemic than people being lazy, a huge component of it is the sheer availability of god-awful food for you and how addictingly 'good' it has been made to be to ensure return customers.