There is also fairly steady migration out of the city [0]. Looks to be related to COVID policy although there is a longer term trend.

If 10% of the population has left, there is a bias towards office workers leaving because they'd probably tend to have more money, WFH policies and people were building based on population increases ... 35% vacancy rate sounds pretty reasonable.

[0] https://sf.gov/data/san-francisco-population-and-migration