The grass cattle can eat (which doesn't need to be planted; most people around me don't regularly plant their pasture) is not stuff people can eat, and can often grow in conditions that can't grow people-food.

Specifically, they can eat stuff that doesn't require constant fertiliser inputs, where as people-food generally does need a lot of fertiliser inputs and needs more intensive herbicide/pesticide application.

A balanced approach is to go, "Hmm, it's probably a good idea to raise cattle, chickens, and other animals, and also to grow all kinds of produce and staple crops as well."