Because there is no free market in housing whatsoever. Owning land doesn't give you the right to build anything. You need planning permission - which means per

Because there is no free market in housing whatsoever. Owning land doesn't give you the right to build anything. You need planning permission - which means permission from the local council, local homeowners and consultation, etc. which gives the NIMBY attitude so much power. There aren't piles of empty houses. There aren't enough houses at all.