Do you think the perception of crime/safety might be an explanation? The difference with three decades ago is the ease of information distribution with social media/internet. Most likely also media coverage has shifted more to crime reporting.

If I'm not mistaken Levitt describes this perception of crime in his book, Freakonomics, as well.

There could be some lag involved. The children of 3 decades ago are now having their own children and are deciding their freedoms. I think crime was lower in the US 6 decades ago than 3, so each generation may be reacting slowly to a perceived level of danger.

I think one of the issues now is that there are many more homes with two working parents. It was one thing 30 years ago to let your kids walk to school, wander around the neighborhood, or whatever, if a parent was at home. But without that safety net, I can see why it's a psychologically challenging attitude for parents. (besides the whole media focus on crime exacerbating things).

(I was born in 1977 and walked or rode my bike to school until 4th grade, when I switched schools. I also had a mom who's rule was "go outside and play. come in for dinner when the street lights turn on." I think this was common across the US until the '90s, especially outside of major metros.