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.
you're replying to someone who said landlords are unnecessary middlemen in the construction of housing. your mocking analogy is "people buying things with credit cards". do you not see how funny a self-own that is?
the landlords are the credit cards in your analogy. people bought things before credit cards existed. people built housing before landlords existed. landlords are as necessary to the building of housing as credit cards are to the buying of toilet paper.
tho I wouldn't be surprised if you thought Buttcoin was necessary for cleaning your shitty ass.