There is an ongoing PBS TV series (also several books and also a website) called “Closer To Truth”. It is hosted by neuroscientist Robert Lawrence Kuhn. He’s featured in one-on-one interviews and panel discussions with the cream of the cream of today’s cosmologists, physicists, philosophers, theologians, psychologists, etc.
Let’s start with the assumption that there are indeed multiple universes as many of those interviewed on “Closer to Truth” have advocated. I’m not convinced they have thought as far outside of the box as perhaps they should have automobile news. Proponents of the multiverse seem to be fixated on a multiverse in space, all universes co-existing pretty much at the same time, as in right now. Little if any thought has been given to a multiverse in time; over time; throughout time.
There is of course the fine-tuning argument that the more universes you have the greater the odds that one will have laws, principles and relationships of physics that will make that universe a bio-friendly universe; a Goldilocks universe. That alone explains the vast improbability of our existence. Another reason however might be that you would philosophically like, on the grounds of fairness and equality, that anything that can happen, should happen.
What’s the point of creating multiple universes instead of just creating one large universe that would be equal in size, and in intelligences that inhabit that one cosmos, to a bunch of universes? Maybe it’s a case of doing it just for the sake of doing it, but that doesn’t seem to be a rational reason for an infallible supernatural deity. In any event, to a deity, is there anything different in principle to creating many universes relative to one universe since to that deity all universes would be connected, a unified whole, even if only in the mind of the creator deity.
The concept of multiple universes seems to be advocated primarily to explain the fact that our Universe is a bio-friendly Universe or a Goldilocks Universe. Our Universe is very finely-tuned in terms of the laws, principles and relationships of physics (and chemistry) to allow life to survive and thrive. The odds that this should be are so astronomically low that anyone betting the family farm would bet that if our Universe were the only Universe it would be lifeless.