It's unfortunate that the one answer to this from a person actually being prescribed "diet and exercise" is saying they don't want to and that comment is currently greyed out.

Because my less than expert observation is this comment is the kind that gets trotted out consistently by cynical systems thinkers who think they've uncovered sinister forces making the population sick on purpose. This seems to ignore that tremendous effort does go into trying to convince people to eat better and exercise more. Money put into youth sports, mandatory gym classes, amateur athletics as their own carveout for nonprofit activity. Lyndon Johnson launched the presidential fitness challenge in 1966. Michelle Obama tried to make this her entire pet project for 8 years while her husband was in office. Other parts of the Internet are full of people like the greyed out comment making the exact opposite observation to yours. They complain that doctors don't take them seriously or give them medicine, refuse surgeries if you're overweight, and are always prescribing diet and exercise.

For what it's worth, and I guess it doesn't have to be worth much, my personal hobbies outside of work have always consisted of sports and fitness. I was into these things well before I ever discovered my first computer. One consequence is most of the informational/entertainment content I consume is sports and fitness focused, including a few podcasts hosted by both coaches and medical doctors, who also make the same counterarguments to your own observation here. Every major medical association out there, national and international standards bodies, primary care physicians themselves, do in fact prescribe preventive measures like diet and exercise, but either the patients and general population ignore these and don't do it anyway, or they don't seek any sort of remedy until they're too far gone in the first place.

There are clearly plenty of environmental factors causing higher levels of diseases of civilization, ranging from the accessibility of sports and recreation facilities in particular places to a poor walking environment to food abundance, but it certainly isn't just this. Plenty of nobility of old got fat eating minimally processed, locally grown foods that their ancestors ate, before cars and concrete existed. We can see the same thing happening to our own pets. They're seeing elevated rates of obesity and hypertension and stuff you'd never see in the wild, and this happens even when they're fed great food and allowed every opportunity to exercise. The unfortunate reality is evolution equipped mammals with an incredible propensity to conserve energy and overeat when the opportunity to do so is available, presumably because such an environment would have largely been seasonal and not permanent in the distant past. We've made it permanent.

I'm not at all trying to say that we can't do anything society-wide. There are obvious differences between nations and regions. There have to be reasons some places do better than others, but I doubt that market forces are one of those things because those are largely the same everywhere, and the entire world has seen diseases of civilization pop up as soon as people have the chance to overeat and live sedentary lives. Hacker News really hates this for some reason, but things like GLP-1 agonists are going to be necessary if you really want to hit everyone that is affected by this. A whole lot of people simply are not going to eat less and move more no matter what incentives you give them.