So, why are you an atheist? Why don’t you believe in a God?
Theists, that are people who believe in a God, have made a rather large claim that a God exists, and since I have not been shown any proof of His existence, and the proof that theists have already put forward has failed under scrutiny, I reject their claim. The claims made by theists have not yet met their burden of proof. Until I’m provided with sufficient evidence and reason, my default position will remain that of disbelief.
When Bertrand Russell, the Welsh philosopher, was asked why he wasn’t a Christian, he had a wonderful response. You can substitute Christian with your own religion and your own God, and his response remains just as valid:
“Because I see no evidence whatever for any of the Christian dogmas. I’ve examined all the stock arguments in favour of the existence of God, and none of them seem to me to be logically valid.”