Possibly the Polish-Americans’ ancestors were speaking regional dialects that differed from the standard language. When Jimmy Carter visited Poland, he had a translator whose Polish was not the standard language, which resulted in some embarrassing mistranslations (Jimmy had “abandoned” America and “lusted” after the Polish people).
No, I met a 20-something here whose parents migrated in 1990 -- so second generation. And his Polish and even ability to speak polish was nonexistent