One Native American language is taught at my nephew's public high school in Northern Michigan (significant community of Native Americans).
It's an elective, among other foreign languages.
It would be nice if more schools chose to do that, but practically speaking, there aren't a lot of people qualified to teach such languages.
Speaking a language natively does not mean you can teach it. There are plenty of native English speakers on this who can't explain why they say things some way, and plenty of others who give wrong explanations.
I would oppose requiring Native American languages in schools, but would love for it to be an option where possible.
The other factor is that those languages have a high difficulty level for monolingual English speakers. The most popular foreign languages in American schools, French and Spanish, are among several languages that are the easiest (but not easy) for English speakers.