The Atheist Perspective
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.
Comments
God designed us to be in fellowship with Him. Thus people have a need to worship, to look outside themselves to worship something greater, wiser, stronger.
The capacity for reverence and worship seems to belong to people by nature. These feelings of reverence, attitudes of worship, and acts of adoration are real. If God does not exist, then these feelings have never, not one time, had a real object.
Which is more reasonable - that all these people have been deluded, or that those who refuse to believe in God are the deluded ones, like the tone-deaf person who denies the existence of music or the color blind person who denies the existence of colors s/he cannot see.