Read the agreement?
The restrictions on Mar-a-Lago were enacted by the Town of Palm Beach Town Council which governs the property's jurisdiction.
In 1993, Donald Trump signed a Special Exception Agreement to convert the "large residential" private estate into a commercial, private social club.
This meant if Trump sold it, that the new owner would not inherit the ability to run a commercial club, but only use it as a private residence.
Thus reflecting the value to a new owner, and not the existing one.