Why not deism?

[GrandizerII]

Feel free to look up modal realism and read a bit on it (if you haven't). The universe/cosmos exists necessarily if you accept the supports for modal realism are true and therefore modal realism is true. If you accept that, then there is no possible world in which not all possible worlds are actual.

But even if you don't go along with modal realism, I don't see why something about the universe cannot exist necessarily and from which all else in existence stems from.

I've read some Leibniz and Plantinga, and the rest is Wikipedia. :-) So all possible worlds exist. This would seem to go way beyond naturalism unless every possible world is causally independent of every other possible world. In that case, we must account for existential causality in each possible world. If something is a causally necessary existent in a possible world, then all causally necessary existents are actual. But then we are just pushing contingency to all possible worlds — what is causally necessary in one world is not causally necessary in another. Wouldn't there still need to be something metaphysically necessary to actualize all possible worlds?

The whole talk about necessity vs contingency can be tricky especially when positing something like modal realism, but the way I look at it is all possible worlds are actualized by necessity because, per the reasoning behind modal realism, you can't have a possible world that is not actual.

If they are spatiotemporally isolated from one another, it does not mean that all these possible worlds aren't part of the same superset world. There is one ultimate actual world in which all these possible local worlds are subsets of, and if they are contingent, then they are contingent on that ultimate world.

The main reason I hold to this view is because I'm a big PSR guy. Why this specific world rather than some other specific world cries for an explanation that traditional theism/deism fails to answer.