I think there are two strong factors here: 1. Nostalgia is a hell of a drug and change is scary. 2. I got mine - time to pull up the ladder. SF is a really w

I think there are two strong factors here: 1. Nostalgia is a hell of a drug and change is scary. 2. I got mine - time to pull up the ladder. SF is a really weird place to live where people want to keep it locked into a scenic ideal that isn't scalable to the population that wants to live and work there. There's also a weird conflux of geographic constraints coupled with a whole boatload of money. Additionally, all of the businesses established in SF have a strong motivation to keep more businesses out to protect their revenues, even if more business would contribute to a stronger economy through long term growth. I think it's fair to say that SF is slowly falling into the ocean, but there's still enough demand and money flowing in that it keeps pushing itself up periodically.