This is because you refuse to believe spiritual evidence, but much like the detractors of Aristarchus, your beliefs are wrong. It defies all reasonable logic that the smartest most advanced creatures would need to invent a placebo for knowledge and security blanket for irrational fears. That it would maintain this 'delusion' for it's entire existence, in order to enable the remarkable accomplishments man has achieved.
If you don't think people will lie to themselves or to others, either for comfort, or out of fear, or any of a host of possible reasons, I wonder how much time you've spent around other people.
If you don't think people will believe the lies that others tell, either because they are trusted (like a parent) or because it fits with a personal bias, I question your understanding of human nature.
If you think people are generally especially rational or logical, you should open your eyes and ears to the world around you.
This isn't just a case of religion. People do the same thing with just about anything you can think of : politics, sex, relationships, work, etc.
It is illogical to think that just because people have believed in thousands of different kinds of higher powers, or supernatural creatures and forces, or magics, or what-have-you, that those extremely varied beliefs must all be based on something real. That the person who believed in Odin the all-father was experiencing the same thing as the person who believes the ghost of their grandfather still wanders their home, and the same as the person who believes they can cause someone bad luck through the force of their will.
Mankind has clearly maintained the same delusions for long periods of time if the major religions of our history are incorrect. Why you think the delusion of, say, ancient Egyptians and their pantheon of gods can be true but that humanity could never delude itself en mass is beyond me.