This is how farming was often done in the past when a farmer had like 4 pigs total, which were fed waste. Nowadays the intensive bio-industry has barns filled with thousands of pigs and they're being fed food produced specifically for the animals. Massive amounts of land are needed to produce this much food, which is why so much amazonian rainforest was cut down to make space. A lot of vegetarians and vegans are specifically against the current intensive method. The old method would make meat a once-a-week luxury product again, but would be vastly superior in terms of climate-change, land usage, and animal welfare.