There are millions of Americans who own what would otherwise be "developable and valued as such" land that became basically worthless with the state passage of various environmental laws (particularly wetlands setback stuff) that make the juice not worth the squeeze except if the location were to become "major urban area" level dense while the municipalities passed zoning laws making it all but impossible for that to ever happen.

I guess when you think about it it's not that the land is less valuable. It's that there's no value left after doing what you'd need (endless engineering and construction hoops, lawyers, court, etc) to extract the value without the government just unilaterally deciding you no longer own the land and backing that up with violence.

Illinois state is in a bad financial position, they can't inflate their way out of it. Financial assets are easier to move than land if things get bad.