It is possible that the Ascians are planning to start a war using Ishgarde and through that maybe they are hoping to awaken the "first" mechanical/primal based hybrid Alexander. Seeing as Ultima was a hybrid in the sense that it was a mechanical creature which drew it power from Ifrit/Titan/Garuda. It's possible that the tecnology of Ultima was discovered through the primal Alexander which could sleep beneath Ishgarde.