That would require them to actually care about the Native Americans, and the history of the USA would indicate there has never been much care for them unless it met the needs of the white man.
Ah yes, the USA, the world's first and unique evil entity. I'm sure if the Native Americans had superior force we'd all be walking hand in hand right now, singing kumbaya.
Now back to reality: The history of humanity would indicate that there has never been much care for the weak unless it met the needs of the mighty. If anything, the USA has been the most benevolent superpower to the weak than any before and likely after (assuming China succeeds us), the unique existence of reservations is proof of that.