It is not a myth. I’ve waited behind some of these people in the checkout line. Very few of them spend money on the kinds of groceries that will stretch a dollar and are actually better for you. Flour, corn meal, potatoes, greens, beans, onions, peppers, corn. Mostly I see prepared kludge, meats, and high fat junk food. And yes, I have seen crab legs and shrimp in abundance.
These things would require them to cook! Far easier to grab something you can eat right out of the box or the bag.
One of the things I've noticed is the prodigious quantity of soda pop they buy.
That crap is poison.