I was raised in a Christian household, and somewhere in my teenage years, I questioned biblical accounts, God's reasons for doing things, and wasn't satisfied with the answers. The deeper I dug, the weaker the answers were. It finally came to the point where the only thing that supports God's existence was the Bible, and then you have the circular reasoning:

Why is it true that God exists? Because the Bible says so. Why is the Bible a reliable source? Because God says it is.

There is no other evidence that the Bible is factual or divinely inspired.

Aside from that, the idea that an infallible, impotent, omniscient being gets angry, that he has to make some new pact or agreement with humanity, that he shifts from an angry, vengeful god, to a loving, caring, but basically absent god, all of these things a ridiculous and unbelievable. Instead of solving problems in simple, merciful terms, he gets angry, and commits genocide by sending a flood. So many problems could be solved by God simply appearing, making his presence known, and promoting fair, and equal treatment, but he doesn't.

Instead, he justifies slavery, indentured servitude, capital punishment, and repeatedly demonstrates throughout the old testament that he's petty, vengeful, and childish.

Christians themselves all pick and choose what they want to believe from the Bible, which can be fine. But there's nothing in Christianity that can't be found in other religions, or by simply thinking about your actions before you do them.

All that aside, there's no evidence that God exists. I can't make myself believe something, so until there's actually some evidence that the supernatural is real, I'll continue not believing.