They don't live in SF. It isn't unheard of to commute two hours for a retail job in SF just to get where you can afford the rent.

Well, there must be also a given number of "middle class" people, that are not top notch programmers, nor "entry level" or "retail".

If we take these as valid data:

https://www.bls.gov/regions/west/news-release/occupationalem...

And set an arbitrary threshold at 45 US$/hour, the amount of people exceeding that are 31.1%, if we set it at 50 US$/hour they are 19.4%.

If we draw another line, those that get less than 25 US$/hour are 42.1% and those that get more than 25 but less than 45 are 26.6%.

So, even if we assume that 40% of people commutes for long distances (and BTW technically are not SF residents), since only between 20% and 30% of San Francisco workers can actually afford it, it still leaves us with 30%-40% of people that must be in a really tight spot.

I'm not an expert in California, but if I understand prop 13 correctly it is possible some of those are people who have lived in SF for many years at the same address - their house is paid off and taxes are minimal so they can afford to live on much less. If your house only costs $400/month to live in ($100 insurance, $100 taxes, $200 other utilities) minimum wage still leaves plenty left over, and presumably if you bought a house 30 years ago you were worth more than minimum wage...

Maybe that would account for a part (I am also not at all an expert in California, so it is just speculation), but those cannot reasonably account for 40% of workers.

I mean, if you live in SF and have a yearly income of "only" 50-60,000 US$ working some 2000 hours at 25-30 $/hour, and you live in a house that you can rent for roughly the same amount or that you can sell for (say) a million, what actually keeps you there?

Maybe you can find somewhere else a similar job, paid in the 15-20 $/hour range, you lose 20,000 on the job but get an additional 40,000 from the rent or from interests on the capital.