Children don't have the patience of parents. They melt down waiting for a bus/transit in snow or summer broiling heat and it becomes a nightmare. I didn't have a car most the time until I had a kid and found quality of life went way up with a car.
I was born in a walkable in Europe. School was 5 minutes (by walk) from home. High school was 10-15 minutes by bus, plus 10 minutes walking to the bus stops. The bus service was very frequent, there was no endless waiting on bus stops in snow or heat. If Communist Poland could pull it of, so could the richest country in the world.
Getting to school works but that's because everyone on the bus is going the same place.
A child can walk to say a cornerstore in the US many places no problem but the parents will be placed under arrest for negligence. Most any other place they'd like to go is most practical with public transit involving a long wait or driving by what appears to the child as a private car chartered at his convenience.
Same thing in Singapore, kids from grade 7 on take public transport to go to school (earlier grade students live close to the school usually). I think Japan is like that too.
