I think you answered your own question in the subject like of this thread.
Why does God exist? Because people's minds make him real to them.
Why is he in everybody's mind? Because religious people can't keep their goddamn mouths shut and keep talking about God.

And what do you believe in, simpleton?
Because for somebody supposedly tied to "reason", you seem to be awfully judgemental.
Anticolay26 has it right.
People are not animals and can feel difference between matters of soul and purely physical sensation. What you are exhibiting here is nothing but immature fit of rage. He loves you none the less.
I really think you should re-take that Biology class. We are the most dangerous
alive today.
We are mammals.
Humans and chimpanzees evolved from a common ancestor.
You are not that special. You'll die and decompose like millions of generations before you.