Because those grazing lands don’t support crops. They support a little bit of grass and in their natural state had herds of animals not too different from cattle grazing on them.

People don’t seem to grok this.

On land with little rain you can raise animals where you give a huge expanse per animal. They eat grass and fertilize and participate in the ecosystem.

If you wanted to do anything else with the land you would have to irrigate nearly every drop of water and many places you can’t actually do that at all.

There aren’t just easy equivalents like you’re trying to pose.