Buddy, you are contradicting yourself with your remark there.if the highest floor units are the last one to sold, they will still be sold isn't it? If the units are already sold, the owners would have lived in the units which is against your "no one wants to live on the highest floor".

Take note that although you or someone else do not want to take the highest floor, there will always be someone or several people who prefer to take the highest floor. The highest floors are always preferable to the lowest floors and the demand is reflected in the pricing of units. If the price is the same with all floors, you would see more empty units at the lower floors.