San Francisco has a limited area that is already fairly built-up. To increase the housing supply, the city can't just build anything, it has to build in a way t

San Francisco has a limited area that is already fairly built-up. To increase the housing supply, the city can't just build anything, it has to build in a way that increases the density of housing. For example if you build four story building where every floor is just one unit, you haven't done much - and San Francisco's high housing costs and appeal to the very wealthy makes such luxury condo development very appealing to private developers. Moreover, developers see the large picture and see that if the housing shortage was actually solved they'd lose the premium they now get so this gives them a further incentive to not actually increase total density by much.