The staples are cheap. You don't substitute hamburger helper for asparagus, you substitute it for potatoes, legumes, and grains. Which are so cheap they're practically free. And nutritious as hell.
The healthiest food also tends to be the among the cheapest. People just don't get the convenience factor, and need to take the time to read a book on basic nutrition and cooking. Even if its just a crock pot or microwave. People lacking the basic knowledge to even correctly feed themselves...how did it come to this?
Giving a huge chunk of the population free sugar water is having an extremely deleterious effect on health, I'd wager.
I know its not practical. I'm just doing a "Gee, wouldn't it be nice..."