[ThrustVectoring]

Because the cost is in satisfying local rent-seeking, rather fundamental physical restrictions. If the cheapest housing unit costs three times as much in SF because of earthquake-proofing, HVAC, and density, then sure, build in Sacramento instead. However, roughly speaking, the price differential is because people in SF voted to have houses that cost three times as much (because they own houses and get to make those decisions consequence-free).