Those things are cheap in the US now?
I know people who don't take their $4/month heart medication prescription and end up hospitalized.
I know people that when faced with the choice of walking around the block for exercise would rather watch Netflix despite their uncontrolled type 2 diabetes and doctor telling them exercise will keep their blood sugar under control.
In my examples this was a person who had a pre-existing dentist who already accepted their insurance - it was literally just the effort to go they couldn’t muster.
The $4 heart medicine was not insurance related. It was already in their medicine cabinet, they just couldn’t muster the energy to set a reminder to take it (or even take it if their spouse reminded them).
And the last one is purely the trade off between Netflix and a walk.
In season vegetables are dirt cheap. If not frozen, prepared, mixed veggies are a couple dollars for 5-6 servings (no need to wash or cut!). Chicken is easy to find at <$3/lb, same with hamburger. Rice and beans are dollars per pound.
The real answer is, like most things that humans do that aren’t good for them (eat too much and end up obese, not exercise, not eat healthy, smoke, drink too much, not take medication or go to the doctor or dentist), is cheap, starchy food is just easier and lower effort.