That's because for someone who requires evidence before belief there's rarely been major unexplained phenomena to convince them of the existance of said power from any source.
I can imagine even the most cognizant person running into problems with assigning things to a god without civilisations aggregated knowledge of concepts like atomic principal, meteorology, astrology, germ theory, social studies.
Imagine seeing tornados, or super cell storm structures, flooding, plague, tsunami's, all without a hint of understanding of weather, or germs, or global tidal movements, knowledge that's only been globally accessible to the common man in literally the last 30 years.
The normal person's aptitude to reject god comes down to the ability to understand and explain anything that would prior be considered an unexplainable phenomena, which relies entirely on their grasp of the combined knowledge derived from all civilisations past.
