Per capita income is 50K. A ton of people in SF have rent control, 10,000 live in housing projects, 20,000 live on section 8 and
30,000 live in SROs. the average income in the projects is 14-25K, same with the SRO population. The cap for section 8 is 60,000 (75% of median household income) which marginally increases depending on how many kids you have. None of the above pay anywhere close to market rate.
Rent control applies to any building that got a rental permit before 1979 which is well over half of the rental stock. People who stayed in the same unit for 2 decades are often paying half of what their next door neighbors that just moved in are paying if not less.
If you just moved to San Francisco and are looking to rent, the actual rates you're paying can be drastically different depending on who you rent from even on the same street or even in the same apartment building. If you moved in to someone's 2br apt and they've lived there 20 years you might be paying as low as 700/month because their rent is 1400/month. If you and a friend took a vacant 2br apartment in the same building though you might be paying 2500 each for the exact same unit the 20 year tenant pays 1400 for.
if you're paying the current market rates in San Francisco city it's simply not affordable to anybody making less than 100K period. And even when you make 100K it's not exactly comfy either.