I'm half way into a book by James C Scott
"The Art of Not Being Governed, An Anarchist History of Upland Southeast Asia"[1][2] where he makes a compelling case for why (hill) people/tribes evolve differently. Not because they are in some sense isolated (and backward). It's research mostly about the tribes escaping China and looking for safety by going to higher grounds. They chose not to have a written language, reject religion, or farming, etc out of necessity and to avoid the encroaching state (which means slavery, etc). He shows that despite the difference in geography and their scatteredness (Burma, Vietnam, Laos, ...) all have certain customs in common (and even they are not all from China).
they are not unaware of civilization or reject "culture" because they are "backward" but have been part of it at some point. And they have chosen to become outcasts either because of heavy tax collection, risk of enslavement or imprisonment. People who flee into higher altitudes and away from what the rest calls "civilization" (the rice growing padi states).
The Sentinelese and Jawari (despite not being hill people) are hunter-gatherers presumably because it allows them to stay independent (enslaved, taxed etc). Their customs and strange ways should be seen as having evolved out of necessity to avoid being absorbed by a different group.
[1] https://libcom.org/files/Art.pdf
[2] https://en.wikipedia.org/wiki/The_Art_of_Not_Being_Governed