One reason for the price drop: Originally, the multi-car garage was filled with expensive sports cars, limos, classic cars, etc., that were part of the deal. Those got removed, so the price went down.
And, in reality, it is not the most expensive house on the U.S. market. This is -- $350 million, centered on the Bel-Air manse that was used as the Beverly Hillbillies TV house, owned by the evil right-wing tycoon Jerry Perenchio, now deceased : https://la.curbed.com/2017/8/7/16109508/bel-air-estate-beverly-hillbillies-perenchio