In many places there are legal procedures available to expropriate by force land from owners that don't make use of their real estate.

Near where I live the local city council has run a campaign for years to get people to notify them about derelict and unoccupied buildings in order for them to be able to expropriate it and resell or lease it to companies or residents that actually wants to use the land.

This is exactly because it is recognized that buying and holding land in areas where land is a scarce resource is not in the public interest.