It's the opportunity cost of the land being used as parking.

Manhattan is one of the few parts of the US where we don't indirectly mandate seven parking spots per car on average. A surface lot ends up costing about $7,000/spot to pave. But at >$1,000,000 per acre garages are used instead. But then that's tens of thousands per spot in construction cost. Underground parking is the most expensive type due to excavation cost. Meanwhile the most convenient parking curbside is offered by the government for free or <$1. Is there something wrong with this picture?