Molecules have no long term memory. There is not buildup of new energy that would get out of control eventually. Nothing about the universe in a mundane observable sense is such that it would be logically untenable for it to have existed forever, and for it to continue to exist forever. This is a perfectly plausible reality that cosmologists actually largely agree on as likely. It just goes "the universe was caused by the universe was caused by the universe..." forever. Simple as that.

Compare to a divine creation: There needs to have existed a god to do the creating, and yet then the god has to have been around forever himself before that (lest there simply be another god to have created him, etc.), and must be equally or nearly as complex as whatever he first created at the beginning in order to have conceived of it and created it all.

So, no matter what way you go from all of the above options, you still eventually admit that something was around forever, if you believe in causality at all (and if you don't, you can imagine an easy analogous argument where "the universe popped out of nowhere on its own" is still the simplest explanation)

Thus, "things being around forever" is not a distinguishing feature of any of these theories, nor can this being likely or not be an objection any of them can rationally make against any of the others.

What DOES distinguish the theories, though, is their differing complexity. If the universe itself has been around forever, we have a system that goes:

X

Where X is as much complexity as is currently in the universe, at least.

If a god is added, then we have:

Y X

Where X is the same as above, but we have now also added another feature--a god--which is separate and thus adds at least SOME additional complexity, since he has some features and is not just a synonym for "universe".

Since negative complexity is nonsense, there are no values you can fill in for the above variables that does not make the god theory more (needlessly) complex, and less elegant, than the "universe ITSELF is just the thing instead that's been around forever" theory.