The reason for San Francisco's high rent/home price is very simple, despite how others like to complicate it more: 1: Its desirable for most people to live here. Possibly the most desirable place in the USA, depending on your tastes. As a result, people are willing to pay more to live here. There are jobs, culture, food, art and much more all in this great city. 2: Rent Control. I wont get too much into it, but my ta…
EDIT: There are a lot of comments about increasing supply as a way to make housing/apartments cheaper in SF. This is not at all well demonstrated, as in NYC new real estate development as continually raised prices and priced out those who had previously resided in those neighborhoods (if they need to move they can no longer afford the cost of living in said neighborhood, esp. if they lived in a rent stabilized or controlled place).
New real estate development can make things cheaper, but we are seeing cities have population influxes and those cities traditionally are land limited for new construction. Those two factors work together to ensure that properties are renovated or rebuilt at higher cost to a wealth class that can afford it. It should be obvious that this is not sustainable, cities that do not provide a sustainable way to live for all classes will collapse.