Owen -
My guess is that, in addition to what SL said, there are too many obstacles. Most of the roads are one-way (at least where I am, in Brooklyn), and there are cars parked nose to tail (well, a foot or two between them) on both sides of the street, with few curb cuts for driveways. There are also trees. Sidewalk space is narrow between the front of property and the street.
David
