Unfortunately people don't take care of themselves because it's expensive too. Most people who don't have a lot of money also don't have a lot of time to prepare food from whole food sources, so they go for inexpensive pre prepared foods, which are awful for you.

Exercise is possible but again requires a lot of time (and energy) that you likely don't have if you're working two 35 hour a week food service jobs (or one, honestly). On top of that the built environment is so hostile to being outside of a car, that the easy free exercise choice of walking places is entirely or effectively impossible in most places.

All that is to say I don't think the blame is on individuals (not that you really said that) for not choosing the healthy options, it's on our society for focusing on work, convenience, and efficiency at the expense of health. Just like everything else here, it's going to be a real challenge to fix because it's to tied into everything else, but I hope we can tackle it.