They are being filled up.
https://www.bullionstar.com/blogs/koos-jansen/guest-post-5-c...
https://www.bullionstar.com/blogs/koos-jansen/guest-post-5-c...
It does make the news when San Francisco's residents start getting driven out of the city. It does make the news when Madison limits the height of buildings downtown. Can you give me an example of people who didn't get a flat tire today? Of course not, because that's just called normal functioning.
but this only happens in the US, right? not anywhere else, like... china?
Also, china doesn't have a property tax, so you can just buy an apartment and sit on it forever, there is no economic pressure (as a property tax is) to put it to productive use.
It is speculated that China will drop the land use grant when they institute a real property tax.