I've never seen this in any of the cities I've lived in.
I grew up in this town :) But I am old and from the country.
versus being in an environment where the parents feel absolutely safe letting their kids run around outside.
I am guessing you are US-based. In Finland, it is very, very safe - yet many people still tend to almost encourage the screens, even though they also say "not too much screen time". Not everyone though. Our neighborhood tends to have a lot of kids wandering around in groups getting up to kid mischief.
When I lived in an apartment, I rarely knew the names of the neighbours that lived directly across the hall.
This is a funny thing. Again, Finns aren't generally very social, so I am seen as weird, but excused as I am Australian. I tend to talk to the neighbors too, even when we don't speak the same language well together. I like the idea of local communities of people knowing each other. Having a BBQ and inviting the neighbors over the fence for a burger. makes life richer.
Has it all been a good culture shock?
To be clear, I grew up in a small town (<1000) then moved to the cities for University and Career. Growing up was just like I described. I had to walk 1.5km to get to school, starting around grade 2, but I knew the families that lived in every other house on the way. I'm glad to get back to the smaller town - it feels a lot more like "home".