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
If Jesus was a historical person, which religious sect do you think he most likely came from?
While holding rattlesnakes and speaking in tongues, have you ever been bitten? Does it hurt?
Is what is morally good commanded by God because it is morally good, or is it morally good because it is commanded by God?
If Fitrah means what is natural, and if having circumcision is Fitrah, does that mean that Allah created us in an unnatural or wrong form that we have to fix it by hand?
By what criteria do you attribute veracity to your faith's sacred text(s,) and thus the basis of that faith? Is that criteria objective?
Atheist Hitler Homer Bible Christ: The Historical Papers of Richard Carrier 1995-2013 Richard Carrier Atheist Humanism: A Very Short Introduction Stephen Law Atheist Why I Am Not a Christian: Four Conclusive Reasons to Reject the Faith Richard Carrier Atheist The God Delusion Richard Dawkins Atheist Atheism: A Philosophical Justification Michael Martin Atheist Sense and Goodness Without God: A Defense of Metaphysical Naturalism Richard Carrier Atheist Not the Impossible Faith Richard Carrier Atheist Proving History: Bayes's Theorem and the Quest for the Historical Jesus Richard Carrier