Earlier quoted context omitted.
The folks living in the reservations have not grown their economies. Economic growth isn't something that happens automatically; you have to go out and start new enterprises, invent new technologies, etc. Some cultures are simply incapable of this and will eventually die out; if you want an extreme example go read "Don't Sleep, There are Snakes" by Daniel Everett.
Perhaps you should look at the conditions that were imposed on these areas. Horrible government education and health care, relocation of individuals resulting in horrific suicide rates, boarding schools that beat students for keeping their culture and language, US government mishandling resources to the point the Dept of Interior was required to cut their internet connection multiple times. Never mind the oil and ura…
https://news.ycombinator.com/item?id=2590535
Stating it that way seems reasonable enough. I haven't read "Don't Sleep, There are Snakes" fully but from summaries I'm guessing the tribes refused to accept Western ways and were comfortable living the way that let them survive for thousands of years. Which is a reasonable thing to do if you could isolate yourself from the rest of humanity and competition.
This article about Northern native tribes https://news.ycombinator.com/item?id=8449134 says that they were far enough along building a settled society of farmers and villages when apocalypse struck and the survivors became roving nomads. Just like all our post-apocalypse movies!