There's some sleight of hand going on here. You can have pasture-raised chickens and pigs (with similar soil benefits; chickens are great at picking out pesky bugs, too), and you can have factory-farmed cows in feed lots.
You _can_, but pasture chicken and pigs aren’t cheap and aren’t really done at a commercial scale. Whereas many conventional beef farmers still raise cows on pasture.
Overall, pasture chicken requires a lot of land and has soil loading issues (too many and the soil gets burned out when the balance of minerals goes off kilter). It’s much harder to overload cows on pasture - it’s obvious when a field is overgrazed.
