Except that it is more profitable to produce housing that is 25% occupied that is priced at > two million a unit than lower priced units that are actually occupied by residents of the city.
The 25% occupancy rate was a fairly recent number from One Rincon Hill With units going for between $700,000 and $30,000,000. That is some of the densest housing in San Francisco.
One of the effects of Prop 13 is that in California when your property goes up in value, your taxes go up no more than 2% annually, and when your property goes down in value you get a new lower cost basis for which to limit your annual increase from. This means that housing shortages that predominantly effect the young and entrepreneurs minimally effect the large voting block of older voters allowing rather unique real estate economic systems to form. Many of them encouraging a concentration of wealth.