The politics are complicated; I have several friends who are working archaeologists in the western US and it is a frequent topic of conversation. Since Kennewick Man, there have been a few other extremely old archaeological sites discovered in the same region of North America that support the hypothesis that a different people occupied these parts of North America at one time. The politics are approximately as follows:

The tribes are given enormous legal latitude and power on the basis that they are residing on their ancestral lands since the beginning of time. This is a working legal assumption absent evidence to the contrary. The Corps of Engineers, Department of Interior, et al need to operate with the consent of the tribes for many parts of their job.

The tribes sometimes use this relationship as leverage to gain a variety of concessions out of the government. The Corps of Engineers needs a good working relationship with the tribes as a practical matter or it makes their job very difficult.

Herein lies the conflict: any scientific evidence that the tribes are not in their ancestral lands undermines their political leverage and so they actively attempt to suppress scientific inquiries that may undermine them. The Corps of Engineers and other government organizations that need the permission of tribes to operate are strongly encouraged by the tribes to maintain the status quo or the tribes will make life difficult for them. It is a clear conflict of interest.

In summary, the tribes have a political and financial incentive to suppress any evidence that they were not the first occupants of their land, and they have the leverage in some parts of government to use the government as their agents to enforce that perspective. Consequently, and unfortunately, a lot of archaeological evidence is quietly destroyed or unreported in that part of the country to avoid being held hostage by the tribes.