Sincere questions from a non parent

So I just finished reading Tracy Moore's piece on the parent who left her kid in the car on purpose for 5 minutes and had the cops called on her by a concerned citizen, and I agree with most of the commenters that she was stretching leaps and bounds to make her point. So, as a non parent I have to ask, when do parents nowadays start leaving their kids alone in general?

I was raised for most of my youth in the 80s by generally negligent parents. They relied on my sister, 8 years my senior, to look after my little brother when it was convenient because he was a baby; but I mostly remember just being left alone. I learned how to cook when I was 6, I taught myself how to do housework (laundry, dishes, etc) around the same age or so. I was frequently left alone in cars, and since kindergarten it was commonplace for my friends and I to walk the half mile to and from school together without adult supervision. I lived in a small enough neighborhood that I would go to dental appointments by myself, and I don't recall any of my friends knowing any different either. I was generally a quiet kid, I'd come home and color or watch PBS and Jeopardy and wait for my parents to come home around 6:00pm or later. By age 9 I was walking clear across cities alone to go to the store, without anyone batting an eyelash.

I'm certainly not saying that my upbringing was the norm, but it seems so vastly different from how some parents raise the alarm at the mere thought of leaving their kids unsupervised in their own back yards now. Are kids still allowed to walk to school alone if the school is close enough? Can they just wander over to a friend's house without supervision? I think we've established that generally people can't leave their kids alone in cars anymore for any reason. I'm just curious as to how much independence kids are allowed nowadays and at what age it's allowed.