I think it comes down to the vanity of man.
We need to see a being who created us in his image and created this planet and the universe just for us (never mind that the planet and our bodies are flawed creations). Because we design things, everything must be designed. Because we desire justice, there must be divine justice. Because we don't want to live a finite existence, we believe in an afterlife.
Bocsius stated earlier that atheists WANT to not believe in god... this might be true for some, but personally I'd love to believe again, if what I believed was truth. Death being a gateway to unending paradise, and all you have to do is believe in some guy or follow some rules? If that didn't sound like an awesome deal, people wouldn't be so willing to sign up for it. This only concerns the beliefs of some religions, though they're the ones getting more popular, and the old testament is being discussed here.
I won't say that there's 100% certainty of no god/creator, and I won't say there must be (and certainly wouldn't be specific). I'm not going to pretend to know more than I can.