This is true to an extent. But at the same time the argument is kind of flawed: can kids safely walk around their neighborhoods nowadays? At least where I lived, the city was nice but there were too many cars and it was unusual to see anyone walking... nevertheless kids walking.
Not sure where you are in the world, but in most of the developed world things have never been safer. So, the answer to your questions is a resounding "yes". Yes, it's safe for kids to walk around their neighborhoods these days.
As a parent, he may be scared of letting kids out on their own because of all the abuses/crimes/accidents against kids - exaggerated by the media.
And then kids do not have enough reasons to move out and play in the neighborhood in a world full of social media, gaming consoles, and the electronics around them to keep them occupied.
Other parents see that there are no kids out there and they do not send kids out there and it becomes a self-fulfilling cycle.
As a kid I remember being out for 4-6 hours every day with other kids and much more if possible. But as a parent, I do not see many kids out there and my kids ends up with very small amount of play time outside (that too mostly with parents) and it is already hard to get them out once the kids are glued to the electronics.