A more "natural" arrangement occurs if we all don't run to large cities chasing glory and gold (which I have done, full disclosure, much to my child-caring woes). There is nothing wrong with nuclear families if you add in something like "nuclear communities".
In many small towns or suburban cities, 3 generations live nearby, with all the aunts and uncles. Help with care is always next door, and children are raised with dozens of frequent visitors or caretakers. I'm quite jealous of the quality of life of my inlaws / extended family for these reasons.
I experienced this in the small town suburb I lived in once. There were always random kids in and out of the house, we'd give them food/water/bandaids whatever. Tell jokes/stories. Even though we aren't related, we all knew each other and our kids just kinda bounced around together. Definitely a cool experience.
I think the media making the entire world out to be some bogeyman waiting to kidnap your child is as much to blame as anything.
I live in a top 10 US city (based on population), and it seems to be as you describe - generations of family living nearby, grandparents, etc. always around to help with the kids. Weekly (at least) family meals, parties where the whole neighborhood is invited, etc. I grew up knowing most of my friends' cousins and grandparents because they were just always around. Even today, I know my neighbors' kids and nephews because they live close by, too.
Sure, I should amend my statement to emphasize _running_ (as in away) rather than _big city_. You can certainly flee family support in search of riches from or to big or small cities.
In many small towns or suburban cities, 3 generations live nearby, with all the aunts and uncles. Help with care is always next door, and children are raised with dozens of frequent visitors or caretakers. I'm quite jealous of the quality of life of my inlaws / extended family for these reasons.