Taxing the buildings incentivizes urban sprawl and blight. People with money to park will park it in empty lots, waiting for the land to increase in value instead of paying the extra property tax to develop it themselves.

The result is a downtown with empty lots, abandoned buildings, and short buildings, right next to skyscrapers making much better use of their footprint and surrounding infrastructure

When a pedestrian has to walk one block further because they're walking past an empty building or empty lot that a rich person has dibs on, it produces negative value for the city