- A month (or year) of time in the apartment for cost $x.
- An option on purchasing more time for cost $y/time unit.
What these "tricks" do is make $x less than $y. That makes sense in the short term when you expect to be able demand higher rent/unit time in the future. When that expectation is no longer likely, it makes sense to lower $y to $x because other landlords will, and they will have less turnover (costs) and the same amount of income.
I look at it like: the fair value for rent is x. The current rent is y > x. If the landlord nominally lowers the rent, they cannot raise it to as high a value next year, and they do not want to do this. Therefore they are incentivised to (effectively) give the tenant money along with the rent to decrease y without changing the nominal rent and giving up on the right to increase it.
Theoretically in a rent controlled market the landlord can't cancel the call option. In practice they might be able to by jumping through some (expensive) hoops, but it should be a reasonable approximation still.
I'm not quite sure what sf/Cali law looks like so I am just taking in generalities about rent controlled markets.
It maybe looks like the landlord is selling a years rent for x and buying a put for the next years rent at y (and recursively options for the later years), but it isn’t really like a put either because it’s really a right-to-try-to-sell rather than a right-to-sell.