ETA relevant links: https://youtube.com/@NotJustBikes https://letgrow.org/
ETA again: I glibly mentioned "being killed by a driver" but of course navigating the typical US built environment if you're under 16 or otherwise unable to drive is a miserable experience in a number of ways even if you survive it. Highways make pedestrian paths unnecessarily roundabout. Parking lots make everything further from everything else. Crossing major roads requires getting drivers to notice and stop for you (harder when you're short!), or waiting through interminable signal cycles, etc.
Anecdotally I spent 2 years of my undergraduate living by myself a 10 minute drive away from University in a little village outside of town. I then moved in with roommates to live walking distance between University and downtown. It's obvious from what time most of my fondest memories are.
I have read that one consequence of the Japanese practice of tearing down buildings and buying new is that you tend to get colocated with many people of the same socioeconomic class and age. We have similar forces going on in the Western world (families may prefer suburbs which also tend to sort by SES, yuppies prefer nice urban areas, etc) but I think in Japan it is a bit more deliberate.