How Atheists explain this phenomenon? Is it only a coincidence? Why the idea of God is the most popular idea in a Godless world?
The human brain naturally (through evolution) likes to order and classify things, the idea that something is simply unknowable is simply unsatisfactory. The concept of God is great way to classify the unknowable. In addition it allows us humans to create a God that we feel reflects our humanity and values. This is the reason that God always seems to be redefined as society's values change.