I think as far as where adult children live that it really is cultural. It may be that they are blue collar folks who have always had extended family close by or they may be rural farm folks who have always had family close by or they may be recent immigrants whose culture dictates that family usually stay close by (immigration notwithstanding).
For my family, this was not that common. I do have some cousins that stayed pretty close to their family farm (one cousin moved an hour or so away and then further later and then came back maybe two hours away). But my immediate family for generations have not lived in the towns we grew up in.
My mom left the family farm at 16 during WWII and went to college about 300 miles away. (My parents had me when they were older, very late 30s. ) She was always close with her parents, but I don’t think she ever actually lived at home again. We visited all the time, though.
My dad was in the Navy in WWII and also went to college and he moved about 200 miles away from his hometown where he met my mom. They ended up settling about 40 miles from his hometown.
He had an older cousin that traveled across the country in the 1930s or so and settled in California.
Growing up I knew very few people who stayed in their hometown. But I think I was probably close enough to the agricultural era of our state (NC) that the opportunities were not on the farm and it was seen as unambitious to stay at home.
I remember watching “Everybody Loves Raymond” in the 90s and thinking how weird it would be to have a house right down the street from your mom. That was not done in my area.