> None of the negotiating parties are willing to reveal up front the maximum concessions
There are 2 notable problems with revealing up front.the maximum concessions.
1) None of them know in detail. They have to negotiate with powerful people whose ability, or willingness, may change from moment to change or may alter between the start of negotiations and the end of negotiations.
2) Giving the information up front would rob extensive, entrenched bureaucracy with centuries or even millennia of history of the personal meeting time and personal control over the negotiations which are the core of their power. Much like the fictional "flappers" of Laputa, their control of information and of the time of their nation's leaders is a major source of their power.
Whether or not they do their jobs well, and many of them do their jobs very well indeed, they're unlikely to willingly surrender their control. And even if the current bureaucracy were stripped of their control, it would re-establish itself very quickly as citizens sought to organize and understand the details of a large and complex environment. So a new bureaucracy of organizing and evaluating the information, and in the end controlling it, would recur very quickly.