Again, I can't stress this enough, we DO NOT know. What is ridiculous is to claim that you do know. This is, as far as I'm aware, something that we are physically completely incapable of understanding with our current level of technology. Slapping something we individually think makes sense onto something that we don't know doesn't make it a fact. It is only a hypothesis until proven otherwise.
That being said, here are some guesses that don't have anything to do with an intelligent god or creator.
Like I said earlier, maybe the universe didn't have a beginning at all. If it is justifiable to you that there was an intelligent being that has existed for an infinite amount of time, it is equally justifiable that the universe has simply always existed. The big bang might just be the start of a new cycle. Eventually it may collapse, and maybe the force from that is enough to cause it to expand outward again.
Another thing I mentioned before, who's to say that the laws of physics functioned in the same way that long ago? In order to make an entire universe, maybe that requires different physics entirely, one's we obviously aren't directly influenced by now, but would be called into question on such a monumental event.
Likewise, have we ever had a "nothing" to test? I promise you that we have never witnessed a literal nothing. "Energy can't be created or destroyed, only transferred" is something that is applicable to our physical world, but "nothing" is not something we know anything about. If you wave your hand around, there's still air there. If you go into a perfect vacuum like space, there is still dust and debris. If there isn't, you probably still dwell within the fabric of spacetime. Which isn't nothing, it is a literal something that is bent and influenced by physical objects. Perhaps "nothing" can't even exist at all, and when it's close enough to existing, something like the big bang occurs to dispel this.
These are only a couple of explanations. But again, they're just guesses. I still wholeheartedly do not know if there was anything before it at all, or if there was what it could be