They aren’t aware of the outside world
Everyone has neighbours, even when they’re some distance away, and they’ll know who they are. If it’s another tribe, they may or may not have friendly relations with them. And many uncontacted tribes have suffered appalling violence in the past from settlers.
They are living in the ‘Stone Age’
All peoples are changing all the time and always have, including uncontacted tribes. Survival doesn’t talk about ‘pristine’ tribes or cultures. They are not backward or ‘Stone Age’, they just live differently.
Reports of uncontacted tribes are faked
Some ‘first contacts’ are acts for the benefit of tourists, but there are actually quite a lot of real uncontacted tribes, and more are ‘discovered’ all the time. Sometimes, they are surprisingly close to people who’ve been in contact for decades, or longer.
They can’t be left alone forever
Whose choice should it be, theirs or ‘ours’? If a people chooses to make contact with wider society, they’ll find a way. The problem is that the belief that they are primitive and incapable of deciding for themselves is still widespread.
If they are contacted, they can have the benefits of ‘our’ way of life
They won’t get the chance. In reality, the future offered by settler society is to ‘join’ at the lowest possible level – often as beggars and prostitutes. History proves that tribal peoples usually end up in a far worse state after contact, often dead.
http://www.uncontactedtribes.org/