You're assuming a baseline of a functional market system.
If you have widespread price-fixing between landlords (say, via everyone using the same algorithm service that gives everyone the same recommendation) then rent control isn't introducing a price fix, it's just changing the level of price fixing.
If you can only rent for $X000, but the rent price is fixed to at least $X500, then for you, there might as well be no availability - the landlord is leaving the place vacant due to the price-fixing.
This is called a cartel. The trouble with cartels is enforcing it. Cartel members cheat all the time by selling for less than the cartel price in order to get a larger share of the market. The setup is unstable as the incentives are much like the Prisoner's Dilemma.
The issue with housing affordability is that the market is often prevented from responding to high demand and low supply by regulation. SF is very restrictive with permitting housing construction, despite the incredibly high rents. It's not that the market forces are failing to incentivize housing construction, it's that developers are prevented from responding to market demand.