Now I'm in Spain and it's dense and I can't even fathom to have a car.
Some major metropolitan areas with subways are like that; I was surprised some U.S. adults go through life without learning to drive. In the places I've lived, I could hardly fathom not having a car.
again - issue with urban sprawl. my nephew has most of his friends within walking/biking distance and while he is quite "glued to the screens" he often goes out briefly telling parents "I'm going out to this or that" (he's 14yo now, started quite independent since he was like 5-ish?)
In the U.S., one factor is the distance from many kids to school, another is the practical reality there may be busy highways to cross between the kid and school even if the distance isn't all that far. Walkability in many U.S. locales is not good. A seasonal issue is much of the U.S. gets very hot in summer and/or very cold in winter. Granted, even if the day's high of 90+ degrees F doesn't kick in by 8 a.m., one could still get to, or home from, school pretty sweaty, never mind cold winter mornings in the teens and 20's. So even kids who could walk need accommodation some of the time.
I spent the 1st 8 years of so of my life in a suburb where I roamed the neighborhood on foot or bike a lot unsupervised, 'free range kids' were normal, and there were pro.s and con.s to that. One anecdotal memory sticks in my mind from when I was a few blocks from home. A stranger in a suit and a nice looking (? luxury?) car stopped and tried hard, persistently, to talk me into getting in his car so he could give me a ride home. I didn't go for it and I'm still here, but little kids are often ill-equipped to face off with an adult, even if the kid's been taught not to do such things. Still wonder if my face would've made it onto a milk carton.
I now live on sort of an 'outside edge of town' suburb road where some other kids live, but our kid wouldn't dream of roaming the neighborhood without a 'guard.' And not because we disallowed it.
Note: go back a few generations and some families had 'amateur farms' and other 'chore generating' things going on, and getting away from home could mean getting away from work and the baleful eye of parental authority. Now that many kids hole up in their 'entertainment center' rooms video-conferencing with their buddies, the drive to walk out the front door is less. My point is, it's not all paranoid parents demanding their kids live as shut-ins.