That stretches the definition of "monopoly" awfully thin. They can always park on the street a couple of blocks away and walk home, like lots of city-dwellers do.

Yeah, it sucks that they've lost something they assumed they'd have forever when they purchased their property. But that's why you need to make sure that the HOA is in good shape when you buy a house that has one. Apparently nobody noticed, for thirty years, that the HOA wasn't paying taxes on its property, or that the wrong address was listed for it. Did they never have an internal audit?