The cheap shit food doesn't help, but you've definitely hit on a big part of it. Walking and jogging are pretty inexpensive.
The cheap shit food is the great majority of it.
You can always out eat your workout.
2 mile run and I burn less than 200 calories. I can undo that in 4 Oreos inside of 10 seconds.
The limiting factor is the diet. The problem is that if you simply reduce a few hundred calories in the obese their body will spend a few hundred calories less. They will lose no weight but they will feel like shit And their hunger and satiety hormones will work to get them to eat. If they fight this long enough (which nearly no one does without medical intervention or supplementation) they will eventually lose a minimal amount of weight and then stall out very rapidly. If they return to eating like they did before they will not just regain the weight but rather regain the weight and more. Attempting and failing weight loss regularly leads to increased weight gain not a return to the previous set point.
The solution to obese weight loss is hormonal. And while shifting diet to whole foods and dumping all the processed crap, especially sugar, absolutely improves that hormonal profile, it isnt the only intervention required in the obese.
The only public obesity campaign that would have been effective in the pandemic is the same one that would have been effective at any other time in our entire lives. Mostly that's to subsidize the right foods and penalize the wrong ones. It would require things that are anathema to American society.
And to subsidize access to guided wt loss clinics or the equivalent.
Or you can push an Obamacare plan that requires all insurance companies to cover gastric surgery free of charge...kidding. sort of.