Why? Because apparently they need some more incentive to keep units occupied. Also, even though a property might be vacant, there’s still imputed rental income there. Its owner is just receiving it in the form of enjoying the unit for himself instead of receiving an actual rent check from a tenant. That imputed rent ought to be taxed like any other income.
Just make property taxes higher for empty buildings. Prorate per month. I thought some country was trying this?
For rentals in general, trying to solve a different problem, we should drastically increase property taxes and then give a discount for primary residence that puts it back to where it is now.