The titles to Indian reservation lands are held by the U.S. government, and the tribes are little more than wards of the government.
That is how it’s implemented NOW, but when the concept was SOLD, they were sovereign nations and that is what the treaties say.
Right now there are millions of Americans like myself who are looking for cheap places to retire and not get harassed by the guvmint. These reservations would represent a perfect intersection of cooperative wills. But the Indian Nations have the right to exclude you and me from living there on the basis of how many drops of blood in your veins is injun blood. Sovereign nations. Otherwise, such a thing would be considered extremely racist.