[solatic]

Because that would ultimately discourage new construction. If you're an investor and you want to invest in a house to hopefully rent out (not keep empty just-in-case for yourself), then you have to factor in the risk of not being able to rent out the property. Having a tax if you fail to rent the house only increases the risk of failing to rent, and thus, makes investing in real estate more risky. Pro-development policies need investment to be less risky, not more risky.

[oakwhiz]

The investment risk does not increase very much if the price is decreased accordingly.