All of that land was available to homestead for over a hundred years. There's a reason no one ever claimed it. The "arable" land--by definition what's farmable--is what they did take, leaving the scrub and desert and marginal grazing lands to the feds, who acquired it all from Mexico via war.
Who acquired it from the indigenous peeps who acquired it from other indigenous groups before them.
The Federal government has been slowly reclaiming land everywhere in the west, under the guise of protecting endangered species. In my area they just expanded a federal park. Then they blocked all further development within the “view shed” of that park. The Columbia gorge area is one prime example of this. See this story about how a couple was forced to tear down their house, then get back to me about how generous the feds are: