It’s an analogy, the specific case doesn’t matter. It demonstrates that infinite does not mean literally everything, it’s possible for some item to be missing from any particular infinite set. In a box of infinite apples you won’t have an orange; in a box of infinite fruit you won’t have a chicken; in an infinite multiverse you by definition won’t have a universe which isn’t part of that multiverse.
It’s an analogy, the specific case doesn’t matter. It demonstrates that infinite does not mean literally everything, it’s possible for some item to be missing from any particular infinite set. In a box of infinite apples you won’t have an orange; in a box of infinite fruit you won’t have a chicken; in an infinite multiverse you by definition won’t have a universe which isn’t part of that multiverse.