Almost everyone walks (and even those who don’t can still use sidewalks, with wheelchairs). “Pedestrian” isn’t some separate class of people.

Also, pedestrians don’t have negative externalities, and don’t take up nearly as much space.

If car-only roads only took up as much room in cities as sidewalks do, I wouldn’t mind them!

> why is a sidewalk for pedestrians by default?

Because pedestrians should have primacy. All areas should be for pedestrians by default, and minimal exceptions made. The majority of the street is a not a minimal exception.