Much of America is inhabited by people who left their place of birth in search of better opportunities elsewhere. And most of this happened quite recently: the USA only consisted of 16 states in 1800 and 45 by 1900. I think this has caused American to be inhabited by people who are much more likely to value independence and (perceived) self-reliance.

What you experience is still quite common. Some of my siblings live 5 minutes from my parents and my nieces & nephews basically stay with their grandparents while their parents are working. A lot of my coworkers claim similar situations as well.