You're absolutely right but Americans don't consider rice + legumes (the standard international poverty meal) to be a "real meal" like the rest of the world.
In general the American diet is very meat-based. Once you hold meat as constant, you realize that fast-food or ultraprocessed food are the cheapest way to get a meat-based meal. E.g. McDonald's is probably the cheapest way to buy a hot meal containing beef (and it used to be even cheaper, you could add fries+coke for just 50c in the past). A lot of poor Americans eat hotdog sausages, microwave meals etc just to get some kind of meat even if it's low quality.
Ready to eat food at larger gas stations has probably replaced some of the cheaper fast food.
Why make 2 stops and all that.
> fast-food or ultraprocessed food are the cheapest way to get a meat-based meal
Are you sure? Let's take the example of the McDonald's Big Mac which is $6.72 [0]
The between the 2 patties, the sandwich contains 25g of protein (not grass fed beef) per sandwich. It's fair to assume the majority of the cost of the ingredients of a burger is the meat. The rest is pretty cheap because you only need a small quantity of it to complete the meal.
Here are prices of Costco grass fed beef patties: [1]
15 patties for $36.31 Each patty contains 26 grams of protein, which is more protein than both patties of the Big Mac combined.
cost per patty = $36.31/15 = $2.42
cost of Big Mac = $6.72
That doesn't even come close to the majority of the cost of the Big Mac. I could do a full analysis of each ingredient, but I think it's clear from this data that fast food is not significantly cheaper, especially considering that the Costco patties are higher quality.
Edit: formatting, and also burgers are super fast and easy to cook at home.
[0] https://www.mac-menus.com/big-mac/ [1] https://sameday.costco.com/store/costco/products/20021199-ki...