Back in the '90s, Trump bought the land in order to convert it into a golf course, but thanks to some pesky red tape that said rich assholes can't buy up acres of woodland for vanity projects designed to attract other rich assholes, the town where the park sits denied his request. That left Trump with a big tract of land that he couldn't do much with except his favorite thing in the world: get a tax break. He donated the land to the state of New York, netting a tax write-off estimated at $100 million.
As great as this worked for Trump, it was terrible for New York, which was left holding a big chunk of land it didn't want. They tried to make it look nice (they really did), but they could only afford $2,500 for annual upkeep, and having no full-time staff, the park soon turned into a nightmare zone of dilapidated buildings, moldy swimming pools, and other scenes that make it resemble a post-nuclear wasteland.