Walkability only applies to the small set of rich people who live in the most expensive part of the city. Growing up in the suburbs, we'd frequently visit family friends clear across the metro area. It would take at worst 15 minutes to drive to and park at their houses for dinner parties. The geographically closest person I know in San Francisco is around 2 miles away, and that's 40+ minutes on foot or more by bus (off commute hours so low frequency, no express service, etc).