Or die. Because, you know, a lot of them die.
However, if the greener grass turns out to be a Mumbai slum or an e-waste site in China, or one of many other terrible but more realistic fates, maybe you'd pass on that opportunity... because, you know, a lot of people die there too.
People in the first world romanticize ancient ways of life, but the reality is that life without basic technology is nasty, brutish, and short.
Another blind spot is that there are degrees of bad. Living in a village in northern Afghanistan is better in a lot of ways than living in Darfur, which is better than Somalia. Honestly, people didn't choose to live in cities and work long hours in factories because we tricked them. They do it because it's better than their previous existence.
Something to consider is that if some members of a society choose the new existence (provided by the new outsiders), then it can undermine the rest of the society.
They are a self-sufficient people that don't seem to be screwing up the world nearly as much as we are... why would we even assume we're superior? Maybe we're just jealous?