There was a big airline crash in the 70s or 80s where a bunch of kids died — they were running a special on kids fares. Many of the kids were unaccompanied on the flight, that was not that unusual at the time.
I spent some time driving a 1970s Jeep Wagoneer recently and it was INSANE how good the visibility was compared to a modern car. Skinny little pillars, small headrests, and a low window belt line so that you had just zero blind spots. Crisp lines to the bodywork so that you knew exactly where every corner of the car was. It was VASTLY smaller than a modern SUV, in a driving position that felt more like a modern sedan. And it was SLOW AS FUARK.
Add that to the fact that towns were smaller, quieter, and slower and it’s no wonder that parents were cool letting kids wander.