If you go to Little Tokyo in Los Angeles, or (so I'm told) Hawaii, the Japanese-Americans there have a similarly frozen culture. In some of the older businesses (those designed to appeal to Japanese-Americans as much as to Japanese tourists) the characters are all of the sort used before World War II, rather than the newer ones that the Japanese government adopted after the war. So too with some of the cuisine. And I suspect that Japanese-Americans who can speak Japanese but whose grandparents were born in the US probably speak in a way very different from the way young Japanese speak today. The culture is not any less "authentic" because the mother country has moved on, just different.
When most Polish immigrants came to US, Poland was still not even an independent country, the US gave them the freedom to assert their Polish identity in a way that they could not even do back in the Motherland.
Polish immigrants historically have been some of the most loyal to their adopted country. But that doesn't mean they had to forget about where they came from.