Taxation doesn't usually make things cheaper.

In this case it does, by effectively removing a portion of the money which can be extracted from tenants from the land market, which can then be redistributed towards other ends. Or you could lower taxes elsewhere. It also minimises impact on development by not taxing improvements on land and directly incentivising densification.

It's an extremely bad tax if you are a land speculator, but the point of the tax is land speculators are the penultimate example of those who become rich for being rich without actually adding value to the system.