They worry that they will lose their “special” status as individual “nations”, which is all PC BS anyway. Various tribes overran and wiped out other tribes long before Europeans came. They were defeated by a stronger tribe; too bad and so sad </sarcasm>.
It is BS. If they are individual nations, then they shouldn’t be allowed to vote in our elections. I mean, we don’t let Mexicans vote in our elections, do we? Oh, wait...