Someone from.. Let's say Sicily (Italy), moves to the USA and has children there who will never live in Italy and/or learn Italian. 50 years later, their (great)grandchildren who were born in the USA, don't speak Italian and couldn't even find Italy on a Map say "I'm Italian because my (great)grandparent was from Italy and I can Pronounce pasta. So, I can speak for all the almost 60M people in Italy too".

Are they Italian? Obviously not. They are statunitensi for us.

Same goes for the other countries. Ex, let's assume I move to Japan, have children there, etc. In 50-60 years my (great)grandchildren who would be born in Japan surrounded by Japanese culture and speaking Japanese language wouldn't be considered Italian in Italy.