Comment by petre

They feed the chickens concentrates and keep them in locked up in "batteries". Some of them die there and they're not removed immediately. There are plenty of horrid videos on Youtube.

Compare that to a soil growing chickens that scrape around for worms and eat grass, corn, wheat and leftovers from the kitchen. In fact that's the best part: you can feed them most most vegetable leftovers as long as they're fresh. Only the younger ones need to be fed some concentrates until they grow up because they're quite vulnerable to diseases carried by other birds, especially pigeons.