Because property is underutilized along our main transit corridors both in and out of the city limits. The tax structures make it so that land owners can sit on basically empty pieces of land right on top of subway stops for minimal cost as long as they don't build. Higher taxes on the land itself would force them to shit or get off the pot. This is why you see land in center city being used as surface parking lots. LVT makes it harder to hold empty plots of land (like Broad and Washington was for so many years) in order to speculate on the future value. Land speculation raises the price for the rest of us who want to actually use the land for housing or business.