the problem happens when an absentee landlord owns a dozen buildings on main street. if a third of their properties are empty and they lower the rent to the point where people will occupy them, it drives down the rent for the other two thirds of their portfolio. if they keep some properties empty to hold the rents artifically high, and they don't have to pay property taxes and management fees on the vacant ones, they can just hold the properties for free while the land value appreciates.