If you look at most big, established cities (Chicago, New York), the bulk of the housing stock tends to have been built in the construction booms of the 1960's-1980's. New construction is a good, but a city will suffer from its bad housing policies for decades after those policies are fixed, because the process of bringing housing supply in line with housing demand is a very slow one.
As an analogy, consider roads: in the D.C. metro area, road construction is about 10 years behind where it needs to be given the population surge, and they have been building flat-out for a decade now. Imagine if they had spent the last 20-30 years not constructing new roads even as the region grew dramatically in population. That's the state of the San Francisco housing market, and indeed the housing markets of most cities that had policies in place over the last several decades that were hostile to development.
As an analogy, consider roads: in the D.C. metro area, road construction is about 10 years behind where it needs to be given the population surge, and they have been building flat-out for a decade now. Imagine if they had spent the last 20-30 years not constructing new roads even as the region grew dramatically in population. That's the state of the San Francisco housing market, and indeed the housing markets of most cities that had policies in place over the last several decades that were hostile to development.