because he's the XII not the CLXVIII it states so in the history they SUMMON him in the primal battle to fight


Soon, the moogles discovered that the distance to the land below was too great for their wings, and it was decided that the journey would be made by rope, the longest that has ever been woven. Thus, the king grasped onto one end of this lifeline as his subjects, one after the next, half clambered, half slid their way to the Promised Land, except for Good King Moggle Mog XII, who had not the means to lower himself.
Mourning their lost king and touched by his sacrifice, the moogles have since abstained from naming a successor to the crown, and ultimately were able to call him back to Eorzea using a mysterious summoning ritual.