Although the Foundation Ball technically took place in all of the halls of the Diamond Palace simultaneously, that was only because there was no hall in the kingdom big enough for all of the nobles to gather within. Even if such a hall were to be built, it wouldn't make for a good place for an event like that - in a massive space that would be required, it would be difficult to maintain safety and order, and the ball could easily descend into chaos. Therefore, instead of trying to squeeze everyone together, the nobles were assigned to various ballrooms, depending on their ranks.