Landlords are not keeping units off the market to drive up prices. There are no landlords who have the pricing power to make that work. There is no landlord that can keep 10% of his inventory off the market to drive up rental prices 11%.
There is, however, in any market a small number of big players, all politically connected, who will conspire against newcomers building new units. A couple years ago stories about that "historic laundromat" in SF were making the rounds, that is very typical.
