Well, I doubt Goku is above manipulating the feels to get the Zenos to agree. They'll be sad they can't have another tournament like this because they erased so many strong fighters, and Goku will cheer them up by offering to use the Super Dragonballs to wish them all back. Then the Grand Priest will be so flustered at the failure of his plans that he botches the wording of the wish, restoring the other six universes that Zeno previously erased as well.