Come to Vietnam sometime, there's plenty of places that are inaccessible to cars, but still get goods and services much cheaper than in car-centric countries.

That's assuming that, first, as a common area, the space roads take up would be only used for walking, and second, that this is a low density area.

Some streets - mostly commercial ones - have heavy foot traffic and sidewalks are always flush with people. Having the whole street available as a pedestrian is much more comfortable for everyone, and it also give spaces for art, activities, lounging areas, etc.