One of the problems of political negotiations without a clear reference point is that the parties, especially the stronger party, can change the rules of the game at will. And the absence of a neutral referee on the field allows such a strong party to get away with regularly moving the goal posts.
This is exactly what is happening in the Palestinian-Israeli talks. It began with the Israelis refusing to accept the principle of the 1967 borders and suspend settlement expansion as a reference point, and continued with Israeli negotiators banning US officials from entering the negotiation room.