Beef is expensive. If you don't have refrigeration, then you milk cows and make butter because butter lasts longer and you can cook with it. Milk you have to use asap, and when you don't have Pasteurization it goes south even faster. And when you need to farm all the grain you can to pay taxes, you are left with the shit at the sides, root veggies, chicken, pork on rare occasions, and tons of butter.

Coq-a-vin is another example. This used to be poor people food; the old chickens that were nothing but tough meat and gristle needed long cook times to make edible. Throw some cheap root veggies in that and you get a good soup that has a decent nutritional base.

The, admittedly racist, stereotype of Black southerners eating watermelon and fried chicken? same thing. Chickens are cheap to raise and breed, you can eat the eggs, feed them kitchen waste, and then when they are no longer productive, eat them. Frying chicken parts in oil is an efficient way to get the most out of the food when every dollar counts. Watermelon was cheap to grow as a side project and many slaves grew it to sell for extra cash.

Hamburger was poverty food, now a staple. Sausage was a way to get edible food out of the offal and slaughterhouse waste with the added benefit that you can store it for weeks/months. Same with Haggis and Shepard's Pie. The cycle is fairly standard.