Why do people deny that God exists, if they can know him by reason?

Why do people deny that God exists, if they can know him by reason?

To know the invisible God is a great challenge for the human mind.

Many are scared off by it. Another reason why some do not want to know God is because they would then have to change their life. Anyone who says that the question about God is meaningless because it cannot be answered is making things too easy for himself. (You Cat Que 5)