San Francisco is 46.7 square miles at the top of a peninsula.

Land there has always been a scarse comodity and pricy.

The expansion south into South SF, Daly City and Pacifica (all San Mateo County) was done using as little land as possible.

The areas that are the subject of "Little Boxes" often had some sideyard. Many parts of "The City" have "zero lot line" housing meaning no sideyard at all. The constructuion style in San Mateo County, at that time and in that place, was reasonable under the circumstances.