Abandoned places/property ownership isn't always as simple as one might think. Some places could be owned by someone like Donald Trump, having a ton of properties to the point where they could just flat-out forget what all they own and one or more of them ends up slipping through the cracks. There was this abandoned house behind my parents' home for years that my mom tracked down and contacted the owner about to see if she could buy it from her for her kids (being me and my sister). The lady forgot that she even owned it, fixed it up and sold it (I didn't want to have anything to do with it myself and my sister got her own place anyway). The same could go with places like these where nothing is done unless people start making a stink about it and find and try to contact owners about it, and even if they can't be found, due to however long certain State processes take, it can take years to legally have something done with a place even if it's declared abandoned/there's legally no owner and the state can do what it wants with it.
Even if a place has decaying, crumbling buildings, the land could still be worth something, hence why a lot of drive-in theatres popped up from probably the 1950s - 1970s, as that was a good way to have land mature to having a facility like that in the meantime.
Some owners could be mentally ill too, hence why nothing is done with properties, and there's probably like eight other reasons why these still exist but I don't really know that much about them.