HI:" lure of the city and fancy sneakers and cellphones."

Reservations can be prison-like and to a young person (now with satellite TV and internet) the difference between what they see"out there" and their depressing surroundings leads to the big exit!!!  
You don't need to be a psychiatrist/sociologist to reason this out.
The only reasonable answer is assimilation into the rest of society.Money alone is not the answer: there has to be the desire to change because change happens even if we don't want it..  

This is happening in the farming communities where the "family farm" is being bought up and farming corporations are growing.