I think it's a two sided chicken and egg type problem: we can only buy what's on our shelves but - having personally come from a country that's hardly famous for its cuisine - I think American food culture ranges from poor to nonexistent. The bar for agricultural and processed products that the average consumer recognizes as edible food is shockingly low whether we're talking about bread or what passes for tomatoes here. There is plenty of ultraprocessed rye breads in Europe, for example, that are far more nutritious and produced at similar industrial scales because most consumers would recoil at the thought of eating Walmart's value brand of sugar bread.

Here in Southern California there are plenty of food desserts that sit adjacent to immigrant enclaves that provide critical mass for amazing grocery stores with a wide variety of higher quality, cheap produce and a diverse collection of nutritious processed and ultraprocessed food simply because that's the stuff that their communities demand. Replacing such a supermarket with a McDonalds would never work within these communities because most families simply don't consider fast food an alternative to their existing diets. These are huge supermarkets that are often similar in size to Costco or Walmart stores (see Shun Fat, 99 Ranch, Zion Market, etc).

We could do with a little more culinary elitism among consumers in my opinion.