Saying that God exists in all metaphysically possible worlds does not provide a ground, but merely a graphic Leibnizian representation of the notion of necessary being.

One can also arrive at the simplicity doctrine via the divine necessity. As maximally perfect, as that than which no greater can be conceived, God must be a metaphysically necessary being, one that cannot not exist. A necessary being is one whose possibility entails its existence, and whose nonexistence entails its impossibility. But what could be the ground of this necessity of existence if not the identity in God of essence and existence, possibility and actuality? Saying that God exists in all metaphysically possible worlds does not provide a ground, but merely a graphic Leibnizian represen...