You do have to ask permission of the landowner to hike/camp on their property. But with the size of some of the cattle on the land (I'm thinking of Texas Longhorns) and the presence of common predators/pests like feral hogs and coyotes, it's not always safe to just wander around.

There's also the water issue. If you run out of water in the west while on your hike/tramp, you're in life-threatening trouble. And there's often no cellular service.