Thrifty cooks have long understood the importance of getting all the mileage they can out of the food they purchase, which of course includes any meat they use. There was little waste in the kitchens of old, and cooks would make use of many things that we tend to throw away today.
In the case of soup, in particular, it was never meant to be made with prime cuts of meat. Quite the contrary. It was meant to stretch the food budget and avoid waste.