That is not very harmful because an apartment is a small box in the sky, and not filling it doesn't use up the land it's on top of, since there's other units in

That is not very harmful because an apartment is a small box in the sky, and not filling it doesn't use up the land it's on top of, since there's other units in the building. Similarly, you can make up for it by adding more small boxes in the sky. Also, they may plan to do this, but investments involve risk and they may go out of business (sell the apartment) if it doesn't actually go like they expect it to.