I think this is a misconception. California has many residents who live in areas that don't have the super wide roads you're thinking it has. It has a wide gamut of roads and many residents (such as myself) are surrounded by more narrow roads. I'm not even in San Francisco. I'm in a suburb in the bay area. (San Carlos)
The following seems to show a road next to a playground in San Carlos.[1] You think thats too narrow a road for an autonomous vehicle to navigate without endangering kids? Have you familiarized yourself with the latest in autonomous / self-driving tech?[2]
I think your fears are overblown or purposely exaggerated.
[1] Laureola Park San Carlos, CA Playground
https://www.youtube.com/watch?v=3g3ITuPd7Gw
[2] The $800M Robo Taxi That Could Beat Uber
https://goo.gl/maps/vokEswX4S8z
I live on that street. The streets adjacent to it are also plagued by a plethora of cars on both sides. Much worse than what streetview is showing because streetview is done midday on weekdays when everyone is gone. (Notice how most of the driveways are empty and recycling cans are out - it's the middle of a Thursday that this was taken) It used to be that people would park with their cars on the curb to give more access but I don't see people doing that anymore.
Certain weekends and at night these streets are very full with cars. Much more than google street view shows. It's deceptively smaller than it appears. It looks as if two cars might be able to slip by but frequently not the case. I can't actually remember the last time I saw two cars go by each other side by side without one pulling over to wait for another to pass on my street in particular. The more main street to the south has the same problem but is even wider.
The streets in particular are pretty wide for this issue but because of street parking being available on both sides, it's an issue.
It has few enough that you can route around them and still get where you're going.