Why should a neighbourhood consisting of single family homes not be walkable?

This is such a neighbourhood from the early 1920s not too far from where I grew up. Take a stroll through it with Street View. It is perfectly walkable.

https://goo.gl/maps/kKqhtNbKDy6oycSi9

The lots are smallish compared to the American standard, though. This is a crowded continent.

Single family zoning isn't simply a car thing. I live in a small, walkable, transit-friendly neighborhood full of crunch eco-liberals, and it is entirely hostile to upzoning for reasons having nothing at all to do with cars; it's a central tool of NIMBYism.