The reasons for that are buried deep in American history, but what it amounts to is that AFTER the Japanese-Americans were released from the government's camps they sought to more fully assimilate their children so that this was less likely to happen to them in the future.
So, nobody taught their kids Japanese language. A few did, but the overwhelming majority didn't.
Even the ladies brought back by GIs from the Orient didn't teach the kids Japanese either. The few Japanese immigrants or long term business representatives here didn't get into the teaching of Japanese. Japanese Americans in Hawaii may well have let their kids learn the local Creoles but they made sure they used English as their FIRST and ONLY language for purposes of education.
By the time you get through the years where the Ise are mostly gone and the Neisei have taken over and dominated JA culture, that third generation ~ and even moreso with the fourth and fifth generation ~ flocked to the professions of accounting, law, medicine, architecture, and to the arts. Japanese American artists and musicians abound in America and live in every city and town.
Those folks don't become Japanese language teachers, or even teachers!
Credentials aren't a problem ~
Thank you for the information.
It seems like something so obscure that the school should not offer it.