Wow! I don't know if this is racism or ignorance. I am gonna give you the benefit of the doubt and assume ignorance. They didn't all suffer the same fate. Some tribes prospered (Cherokee, those not forced of land with gold) and some were brutally treated (Apache, Sioux and so on). It's perspective. US Government recognizes 500 some tribes as sovereign States, yet they ignore the treaties they signed with them. Federal Government assumed responsibility for them. Then proceeded to screw them over and over. Be it the Dawes Act that allowed the Federal Government to auction of land that were part of Reservations. Federal Government auctioned off the fertile land in the reservations. If you were Sioux, you lost the Black Hills, and to this day the Federal Government has failed to return the Black Hills back to the Sioux, as the Supreme Court ruled, rather they offered payment which has now a value of $1 billion.
They have useless land because Federal Government took the fertile land, you really should read United States v. Sioux Nation of Indians in which they point out the conflict of interest the Federal Government has worked by for the last 125 years. That it's impossible for Uncle Sam to be a protectors of a people, their lands and their natural resources.. while at the same time having the power to take their land. Sioux's reservation use to extend Missouri River to the Black Hills (Half of South Dakota). Black Hills and Badlands are rich in natural resources. That's the difference between being rich and poor for them.
Then Bureau of Indian Affairs being woefully underfund for the last 100 years which has lead to as you call it a "inferior culture". They didn't get funding for education like you did, they didn't access to decent health care a person in a city gets. They were basically excluded from the changes we benefited from. Substandard education and lack of jobs leads to other issues that effect them as well. It's a vicious cycle.
So it's not like they are 100% at fault themselves. The system that said was going to protect them, let them down..