[jw_]

Governments set rules which directly affect markets - housing in particular is subject to tons of planning and manipulation by government. They absolutely can change supply.

Want to bring on more high-density housing? Change zoning rules so it is easier to get permits.

Housing regulations tend to be extremely local and I'm not a SF resident, but it is stunningly naive to claim that "housing supply" cannot be influenced by government. I realize Americans love to hate them, but city planning is one thing that governments are actually really helpful to have manage.