Why don’t you believe in the Bible or the Bhagavad Gita? Why don’t you believe in those gods?
Let me guess, If your answer is quite close to what I’m assuming then congratulations. You’re now one step closer to understanding why Atheists don’t believe in the existence of your god or any of the others that mankind has dreamed up.
Like Stephen Roberts once said: “I contend that we are both atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.”