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.
Yep, a 100% income tax rate on zero income is zero. It seems a lot of reddit's financial incompetence is spilling over to lemmy.
Also, property taxes exist and are being paid already...
"Income tax on no income" is exactly what imputed income is, as mentioned by OP. Free perks from an employer are, for example, (in the US), taxed as income.