Because humans have evolved the capacity and inclination to build mental models of their world (both their physical world and their social world), and the simplest model to build (integrating both the physical and the social world) is what we call a religion. But models are only true insofar as they survive only valid tests. We did not learn which tests those were until the Scientific Revolution and we have only recently begun applying those tests in the proper way to the components of religious worldviews. And most people aren't even applying those tests at all, but preferring instead what's simple and easy to believe, to what's actually true.
Why is there religion?
The Atheist Perspective
Does male seed come from between the back and the ribs? What does 86:7 mean?
Are all presuppositions equally valid? If not, how does one determine which are more valid than others?
You say god cannot lie? He said that Adam and Eve would die if they ate from the 'Tree'.. yet they did not die. He said nothing about sin, he said that they would die.
Answers: Muslim, Christian
In "The Prince of Egypt", is Moses depicted accurately according to Islam?
What happens to people who don't accept what you claim?
Answers: Atheist, Christian
Atheist Atheism: A Philosophical Justification Michael Martin Atheist Not the Impossible Faith Richard Carrier Atheist Proving History: Bayes's Theorem and the Quest for the Historical Jesus Richard Carrier Atheist Why I Am Not a Christian: Four Conclusive Reasons to Reject the Faith Richard Carrier Atheist God Is Not Great: How Religion Poisons Everything Christopher Hitchens Atheist The End of Faith: Religion, Terror, and the Future of Reason Sam Harris Atheist Humanism: A Very Short Introduction Stephen Law Atheist Sense and Goodness Without God: A Defense of Metaphysical Naturalism Richard Carrier