Because of the laws around new buildings, rent control advocates have an incentive to prevent old buildings from being redeveloped: if they are redeveloped then there will be fewer rent controlled units! This does regularly play out in the politics of development in the area[0].

Then when rent controlled unit can be redeveloped, there's a desire to allocate various percentages to different income levels. This means that some units have less income for the same cost so it's hard to balance meaning fewer projects get off the ground.

Now there's even further issues about development as a right vs requiring a use permit...

So, there's a lot of contributors, but the political impact of the politics of rent control is significant.

[0] https://www.berkeleyside.org/2021/07/28/uc-berkeley-settleme...

It’s doesn’t take a genius to see see that being a landlord in SF is an ugly prospect.

70% of housing units in SF are still rent controlled. The negative influence of price controls are still felt. Not to mention, repeated attempts to repeal Costa-Hawkins means the threat of rent control is still hanging over developers heads.