It's so easy to play God hovering in the skies, and make decisions for these people's future, isn't it? Maybe they actually don't enjoy 50+% child mortality, dying of appendicitis, and having to barter a truckload of plantains for a pot and a steel machete. Why don't they send someone on the ground, to explain to them that there's a big world out there that can change their ways forever, and give them a choice whethe…
Well, you could not simply explain it to them, you would have to show it to some of them, and let them live the life, before they could make an informed decision. Perhaps the best advice would be to contact other tribes that have been assimilated, and see how they feel about the process. Would they go back, if they could?
Individuals have been taken from tribes and allowed to integrate into western society.
They usually choose to go back.