I loosely agree in principle. However, tribal groups in the US operate as their own little semi-autonomous ethno-states with a bizarre amount of oversight from

I loosely agree in principle. However, tribal groups in the US operate as their own little semi-autonomous ethno-states with a bizarre amount of oversight from the Bureau of Indian Affairs but still have a lot of latitude. There's a dodgy history of researchers lying to native groups in order to get DNA samples(including promising but not delivering medical services, so there's a lot of reticence around participation. There's also issuers around ancestral rights to land which could be complicated by DNA testing, and all of the tribes are intimately familiar with how the government handled the Osage Indian murders, which involved odd elements of heredity and weird legal stuff. Tribes, in places, with all of this stuff swirling around want to embargo participation in this research. The only way to keep their groups DNA out of the research is to stop any and all members from participating. TL;DR it's complicated and researchers in the past shit in the pool.