That is the will of the bound Entities of the Book. To go to the king of Vrondi would mean he would most likely destroy them as they are rather malicious entities. The king of Nero is perhaps the most morally questionable, and has the most to gain by taking the book from R'lyeh. This would also mean reason for Tearanari to go to war with Nero if he does not return the book. But either way they could believe R'lyeh was always an Agent of Nero who was used as a pawn to acquire these treasures of the Tearanari...

Thus possibly plunging the world into war between two nations with three caught in between. All the while the Entities within the book gain power by starting this war, enough to mass an undying army for the Nero to battle engulf the world in their vision. And soon all will be under the spell of undeath, and life as we know it shall cease to be. The King of Nero becomes the new "God" and the Entities are pleased to begin the invasion of the next world, Earth, with their new Servant. Or so the plan goes, as they come from the outer realms to entice lesser beings to share their vision of the perfect world.

And if you can't tell by now, R'lyeh, and his Book is completely Lovecraftian.