I could answer this question simply, by saying: because I no longer believe in God. But the reason this belief slowly ebbed and changed a young, conservative, fundamentalist Catholic into a fire-breathing liberal atheist was primarily the fact that the claims of religion are wrong.
If you pray every day for God to change your life, to get rid of your bad habits, your sins, your problems and nothing happens; if you see how restrictive and unnatural the rules your religion has; if you start to see how absurd it is for people wearing special gowns and hats to get some special say; if you come to understand that you are being told what to think, what to do by people with absolutely no grasp on reality; in essence if you find out that the God-voice you listened to was yourself and that religion is the biggest game of let’s pretend in the world..
Well then you stop believing.
And I’ve been better for it every step of the way.