SF was a one trick town, software, that software wealth in the later stages was built on low interest rates and cheap money. That is no longer the case, and SF will end up going the way of Detroit.
Hasn't SF been going through boom and bust cycles since 1849? A gold rush begins, starry-eyed people move in with big dreams, most don't make it and have to leave, a few lock in real estate and get to rent seek the next batch of space cadets. Rinse and repeat.