Kudos to you Stranger 2 for raising the issue of native languages in the US. Same can be said for Canada and South America for that matter where Spanish replaced the indigenous languages.

The simpliest politically correct answer is the assimilation policies that put 'Indians' in residential schools to christianize and teach them civilized ways. The cost is still being felt as the effects of residential school abuses and government genesidal policies cross generations.

In my ancestral tribe here in Canada we only have a handful of fluent speakers left. Many survivors of residental schools, where they were whipped for speaking their language, are attempted to bring it back but it is a hard battle.

I don't know the numbers in the US but it Canada there are nearly 300 distinct aboriginal language groups though few of those have any remaining speakers. It is a sad reality of the distructive effectis of colonization.

Sorry for going off topic but it isn't often an opportunity to discuss issues relative to aboriginal people hits the boards.