Most theists argue that God is necessary to explain how the universe came to exist. Of course, this doesn't make sense because it's a mystery why "God" can exist without a cause and we can't (and some theists do come up with pretty elaborate explanations for that, but I've never seen one that doesn't just add its own plotholes).
Another reason I don't find a perfect God to be a satisfactory explanation - benevolence aside - is that a perfect being shouldn't be able to create something arbitrary, like the rules of physics and the universe's initial state. Why are they one way and not another? How could a being made only of perfection choose something unless it was the best, and how is it best? No matter what we suppose God's objective is, it doesn't seem like the way things are is the best way.
But for many years, I didn't have a better answer. It seemed impossible to say the universe didn't have a cause, because, well, what could its initial state have been? The initial state of the universe, which didn't need any creator or any cause? To get such special privileges, I thought this state had to make sense somehow. There had to be nothing arbitrary about it. But aside from states which obviously weren't the one (a world where nothing exists; a world where all souls were stuck in the same experience loop with no agency), I couldn't conceive of a non-arbitrary state. So I had pretty much resigned to the conclusion that the universe started out in a random state because there was no such thing as a non-random one.
Until now. I finally get it.
Every possible starting state exists. There are an infinite number of universes unreachable to each other. Everything is real. Nothing is arbitrary.
In practical terms, the world remains arbitrary since we can't access the others, the parts that are necessary to see how it's possible; but at long last, it makes sense to me how our world can be arbitrary.
I'm kind of embarrassed that it too me so long to come to believe this because I actually heard the Cosmic Slot Machine idea expressed way back when I was Catholic. I guess back then I was still clinging to God, and since the atheist expressing it didn't articulate to me why God couldn't work as an explanation, I forgot about it until I thought of it again just recently.