The seasoned appraisers destroyed Trump's claims. The property cannot be developed. Trump traded away all of the value of the property to get it rezoned to a beach club. The comparable sales that the Trump Family used to make their claims were all unrestricted properties.
Added to which, the main residence is designated as a "historical property" meaning it cannot be torn down, renovated, or substantially altered or updated, and since the main building is now 100 years old, or more, upkeep and repairs are substantial, and all must be approved by the local historical society. Who is their right mind is going to spend $1 billion or more on a property they can't develop, featuring an aging and expensive historical home, you cannot tear down, renovate or update?
The property was originally left to the federal government which couldn't afford to maintain it and put it on the market, where it sat for years before Trump bought it for $7 million. At that time, he could have developed it and sold it, but not any more.
The local residents didn't want Trump putting up one of his cheap ass, bankrupt, golf resorts and wrecking the neighbourhood property values. That's why Trump was precluded from developing the property.