At one time, and when the first concepts of God appeared, it is rather obvious that human knowledge was thin on the ground - as to what comprised a human (physically and their inner nature) and what comprised reality external to us. Let alone the rather obvious lack of knowledge as to what occurred before any human was born - given that there was mostly only the oral transmission of anything available then - so hardly likely to be without some bias or to fully represent the past.
And until science came along, humans had little ammunition to form rational views as to themselves and reality as a whole. So if God was a concept that had great appeal and apparently as to answering all our questions - even if many answers might be made up, given the varieties available - guess which side is winning the argument now? And in which we trust?