As someone who knows a few property owners in San Francisco this is a common thing. People in tech make peanuts compared to who is holding property in the city. Most of these wealthy people don't rent because rent control will bring down the value of their property (you can't evict the tenants).

We're talking about international levels of wealth, these same people have multiple pieces of property in Hong Kong which makes San Francisco look dirt cheap.

I know a few property owners in San Francisco and this is the first I've heard of it. Sounds like an urban legend.

Are the people you know single or two home owners? I’m talking about multi home owners in the Bay Area (4+) with property in the most expensive cities in the world. That’s a very different social class than a Bay Area home owner.

The ones who do rent usually hire an agency to take care of the headaches for them.

I might have been thinking of a different definition of 'common' than you were. I don't doubt that more than one person like this exists, but nobody who has attempted to study this has found that the vacancy rate is significant. e.g http://www.spur.org/sites/default/files/publications_pdfs/SP... (from 2014), https://www.mercurynews.com/2018/03/12/empty-homes-a-califor... (actual data from the Census is at https://www.census.gov/housing/hvs/data/rates.html)

It happens in other cities, so it would be odd if it's not happening in SF too.