One problem is the loss of the newer generations as they begin to view themselves as American rather than of their parents cultural heritage. It tends to work this way (using Greeks as a random example):
1st Generation: Is born in Greece, a native Greek speaker, and moves to America and learns English as a second language. Helps to found or attends a Greek Orthodox church, insists on predominately Greek as the liturgical language, and emphasizes Greek culture. Views being Orthodox as synonomous with being Greek.
2nd Generation: Is born in America, a native English speaker, but taught Greek in the home and at church as well. Is raised Greek Orthodox and encouraged to find a Greek spouse. Identifies himself as both Greek and American, favors a balanced use of each as liturgical languages, and enjoys both American and Greek culture. Views being Orthodox as his family tradition, but is not judgemental toward other Christian faiths.
3rd Generation: Is born American, a native English speaker, and only knows some words and phrases in Greek. Is raised Greek Orthodox, but finding his own religious path is tolerated as long as he remains Christian, and is encouraged to just marry a good woman. Enjoys hearing a bit of Greek but favors mostly English as the liturgical language, and considers himself American with Greek heritage. Views being Orthodox as comfortable since it was how was raised, but is open minded to other faiths, and would attend services with his spouse if she weren’t Orthodox.
From here on in succeeding generations he may convert to another faith after college, chose his spouse’s faith, or lose his beliefs all together. He may also resent his grandparents, or possibly still parents, insistence on attending a Greek Orthodox church since he doesn’t view himself as Greek, and seek a church that’s more mainstream for American culture, again often with a spouse.