which is the result of policies that make construction extremely expensive or straight up prohibited.

So you're assuming the same owner owned the building for several years if not decades? You do realize real estate is a market just like any other, you buy at the market price, finance that purchase by borrowing money from banks, finally you rent it out to recover some of the monthly finance costs, taxes and maintenance expenses. To continue saying landlords this landlords that makes you sound like you discovered a hidden truth that explains away the issues related to the high prices we're seeing. In fact most likely majority of real estate investors in the Bay Area are earning very nominal returns on their investment compared to other markets, see local housing price growth rates.