We could change the zoning laws so that it isn't illegal, though.

One of the ways you can reduce cars is by zoning to allow greater density, which enables forms of transit which are more space-efficient than cars are. It's a chicken and egg problem, but people will be crying out for better cycle ways and trains and buses if housing becomes more dense.

Also, having commercial spread throughout residential areas reduces the amount of travel between areas, because you don't need to go far to get to the amenities you want.

It's a bit strange to give Japan's lower cars per capita as a rationale for this, when surely the reason there are fewer cars per capita is because people have access to their daily necessities without a car because of more permissive zoning.