Well it's a combination of tech companies liking the bay area location and the supply of any kind of real estate being artificially limited by NIMBYs. We can "solve" this be either reducing demand or increasing supply. To me decreasing demand seems like a terrible solution. You want people to live in your city. It's insane! Something happened a few decades ago where we started seeing cities as "completed" and any change from that state is seen as bad and"loss of character". Cities are changing, living things. If we prevent the change the city dies.