Can you tell us how and why the universe exists? NO! You cannot. So what makes you the expert? There may well have been a big bang. No one knows for sure. But even if there was was, you have no idea how or why it happened. God is just as valid a theory as anything science can come up with. Tell me I'm wrong.
It is exactly the "how" questions that science addresses.
Can you tell us why the Christian gawds allowed their bibles to be altered by the corruptible hand of man?
It is not logically possible to say or think that your polytheistic gawds are the only gawds that don't exist.
Your polytheistic gawds are merely one conception of gawds. We are privileged to consider reality, but only the universe that actually exists can be
fruitfully considered. How do we assign confidence to what is real and what is simply imaginary?
Evidence and reason. These are our only tools for that task. Thankfully, they appear to work pretty well, at least for those of us not bound to a precommittment to your dogma.
Millennia of philosophers and theologians have invented countless elaborate and ultimately futile models of reality and truth, with next to no positive impact on the human condition. Science in dramatic contrast is among the youngest of human of human endeavors, and yet has achieved things no previous discipline has approached. It has fed the hungry, cured disease, created technology that four generations ago would have been unimaginable. It has literally changed our world, while religions like Christianity and Islam have done little more than churn human misfortune in a static embrace of past error. Unlike all the philosophies and religions that came before it, science actually works.