Several interesting points - when children are all about the same age, go to the same local school and other activities, and so know each other, the families cannot help but mix - things like “you’re going to the soccer game? Can you take Sam, I have to run an errand.” that sort of stuff creates bonds.
In the past 20 or 30 years, families are MUCH smaller - 1 or 2 vs 3 or 4 - and the odds that neighbours have kids old enough to play together is less; another trend is that newer suburbs seem to be built without alleys to economize land use; the garage is direct attached on the front of the narrow house, so there is rarely a useful porch and the live-in part of the house is set back an extra 25 or more feet and not too visible - and people drive right into the garage thanks to remote door openers. With fewer corner stores and mostly remote malls, people drive everywhere (unless they have a dog to walk). Heck, my current location does not even have sidewalks. There’s so much less reason and oportunity to interact with your neighbours, and as I mentioned - with air conditioning, less reason to out in the back yard too.
The immigrant thing is true too - less in common and inability to communicate. I like to say I live in an upscale neighbourhood; many of the neighbours own two taxis.