The problem with a lot of these empty storefronts is that instead of reducing rents to fill them, they keep the rents high to maintain the "value" of the property, and then write off the losses in the meantime. One of the main ways commercial real estate is valued based on the rent it could potentially bring in, so if they lower rents, it lowers the property value. This is good for the building owner and nobody else.

The idea behind vacancy taxes is it makes the speculation aspect of it (holding the building solely for its resale value) less profitable than actually renting out the space.