One question, that isn't often discussed, is how many homes are bought to live in vs. bought as investments and rented. Either way, monthly mortgage or rent is going up, but I wonder how much of the movement in the market is due to real estate investors vs. home owners.
Or bought as investments and not rented out (I hear a lot of anecdotes about this).
More and more, NYC, London and SF are the real estate equivalent of buying gold, but way more profitable. The most interesting thing about this property my brother recently staged is that it was on the market for about $5-6 million until just before the 2008 crash. After the crash, it and many many apartments just like it skyrocketed in value as the economy crumbled. Basically lots of very very rich people, often Russian and Chinese, but not exclusively those nationalities, expatriated money to SF, NYC and London to buy real estate as a relatively safe store of value.
A good friend of my father (who lives in Brazil) is worth several hundred million and he owns an apartment in NYC worth several million that no one lives in. Between he and his family, they probably use it for at most one month per year.
That only counts for part of the problem. Something like 5-10% of the SF housing stock to which rent control laws is applicable is kept off the market because landlords prefer not to deal with the hassle of tenants rights. I forget the exact figure.