Mate, I've seen long-term immigrants not just of my own nation but other nations who returned and was even myself an immigrant of my own nation for over 2 decades abroad, and after 2 or 3 decades people living abroad are already culturally and even in values different from their countrymen, due to a mix of partially absorbing the values and way of being in life and society of were they live, and because their own country kept on changing over time generally in a different way in which they themselves change (it's quite funny how they have ideas about how their own country of birth is that don't really match the reality and look silly and outdated to the people actually living there).

This is a mere 2 or 3 decades for people who actually grew up in their nation of origin.

People 2 or 3 generations away from said nation are not only descendants of immigrants with a deviating cultural framework as describe above, but they have grown up in a different nation (and from all my observations living in a couple of countries, people culturally tend to be closer to the country they grew up in more than the country of their parents) and at least their parents and possibly their grandparents were already people who grew up in a different nation and only knew about the nation of their ancestors via 2nd or 3rd hand accounts.

Whatever "culture" and "value" they have from their ancestors' nation of origin is a thin slice, deeply degraded (often charicaturally so - note the mention of spaghetti eating to mean "culturally italian", something which would make me Italian and my Italian ancestors if any came over during the Roman Empire) and severelly outdated (a century or more) version of the culture and values of the nation of origin of their ancestors.

The difference for example between an American of Italian ancestry and one of Irish ancestry is token if that much compared to the difference between an actual modern Italian and an Irish: American-Italian, American-Irish and so on are but sub-cultures of the United States of America culture and draw most of their ways and values from that one, not from the cultures of the countries of origin of their great-grandparents.