I honestly do not have an exact answer, but I am thinking it has to do with: 1. SF is a city with high population density. It is only second to NYC. 2. Mild c

I honestly do not have an exact answer, but I am thinking it has to do with: 1. SF is a city with high population density. It is only second to NYC. 2. Mild climate. Without harsh winters, you can sleep outside year round. 3. High cost of living. If someone falls under hard times and does not have the means to relocate, the high cost of living could be crushing.