This behavior is probably overrepresented in the bougie places reporters live.
I live in Redmond, WA. Bougie? My rube Midwestern ass thinks so. And there are feral kids all over my neighborhood. Plenty of kids walking to school in groups, or solo. Neighbor kids talk about riding the bus/train to places. Granted, there are a lot of immigrant families around here (hello, Microsoft, et al.), and I'm sure that skews things.
I've noticed the less American and less wealthy people are, the more normal their kids interact with the world, i.e. "free range".
I don't know what it is about rich white people and freaky helicopter parenting. I also notice it with homeschooling and those crazy borderline eating disorder diets. There seems to be an association there between rich white people and pushing self-destructive behavior on kids.
Whenever these conversations come up, I've always noted that they don't really seem to apply to the PNW. My neighborhood (in Seattle proper) has lots of kids running around as well. Neighborhood kids will stop by to pickup my son and whisk him off to some adventure down the block. Getting your kid back involves listening for the correct sounding screams of joy as you walk around and figure out whose yard they are in.
Seattle also has a pretty decent policy around the radius for kids walking to school, so there are always gaggles of kids walking together to and from school for elementary and even some middle schoolers. The high schools are spaced far enough out that kids use buses at that age.
My coworkers in lower CoL areas seem mystified why I'm paying an arm and a leg to live in Seattle to raise a kid. And yeah there are some serious downsides (20-30k a year daycare, restaurants are too expensive to go out to often, even take out is insane), but there are kids playing soccer in the streets after school and kids setting up lemonade stands in the park.
That's what I'm paying for - A city that is built for people to live in, not just for cars to drive around.