Demographic shifts make suburban families too sparse to support children friend groups. Denser cities are increasingly financially impossible for families to move in.
Perfect summer night and there is not a person to be seen. They felt like they were walking around in some kind of zombie horror movie that all the people had vanished.
It feels as though people slowly learned that they could get away with not introducing themselves to their neighbors, invite them over for dinner, and other activities that were once assumed.
Anecdata but I think this is what the parent comment is asserting anyway.
As compared to what I heard from the older neighbors, when they had kids, all the others around also had kids. So many in fact that all the neighbors had doors in their backyards that opened into all the other neighbors yards, so the kids would just run around without having to go into the streets.