Are you referring to German American communities? If so, the answer might be most of these communities were settled by people who didn't speak hoch Deutsch which was the language the educated and well bred people spoke. They spoke various dialects of platt Deutsch. The Amish, for example, speak in a different dialect. Dialects were very localized over 100 years ago in Germany when most of the immigration took place. For that matter, they were quite localized in the US. Consider, for example, Maine, Tennessee, the Ozarks, and the deep south. Huge difference in words and pronunciations.