Cars are not the problem it's fearful parents.

When I grew up there were all cars on the streets, and before cars there were horse and carts which had their own dangers. Over the last 150 years the distance that parents have allowed their children to roam has gradually diminished from many miles to essentially be the other room.

I feel this is more a product of our risk obsessed society, everything is about analysing and taking action to reduce risk. You can hear it everywhere, risk reduction, risk based analysis etc.

Edit: and in the interest of full disclosure I'm a father of 3 and know exactly how hard this is. I can't imagine me being comfortable with what I got up to as a child and that's the tragedy.