If you believe that you will never make more money than the government can pay you, I can see why that would be a demotivating. However, if you believe you have a very good chance at being able to earn more by wages, in particular significantly more, than this line of reasoning will not stand. Very few people will take a course of action that they think will keep them impoverished for the next 20-50 years when they fel they have better options.
So, if your reason holds, why would people on reservations feel the best they can ever do financially is no better than government-sponsored poverty?
What were their chances of advancement to, say, twice what they could make from the government? Do you have Native American managers? Did you single any of them out for mentoring or advancement? Or, did they find a sea of almost all white managers over a native population?
Again, why would they choose a life of poverty if they thought they could have more? You keep repeating "why bother try for more", but you don't answer "why settle for poverty"? They don't like having new cars/trucks, larger houses, better food?
You see the same thing in urban areas, where youth who believe they will never get a fair chance refer to their more optimistic contemporaries as sell-outs, doomed to failure against a stacked deck (they are more often right than not, but not always). I know enough about the urban areas to know racism plays a very big part of this belief; they feel the deck is stacked, so they deal out of the game. They don't like being impoverished, but see little prospect for anything else. Do you have a reason to believe it is different on reservations?
By contrast, I never saw a poor white kid called a sell-out for succeeding in school. Have you? If not, what do you think factors into it?
Poverty takes it toll on everyone. How would being more impoverished help these people? Or, are you supporting jobs programs for them?
Looking at economic mobility, West Virginia comes out pretty well:
https://www.nytimes.com/2013/07/22/...-matters.html?pagewanted=all&_r=3&#map-search
An interesting quote:
How do you distinguish between a problem with the welfare system, and a problem whose symptoms are primarily visible in people on welfare?