Because there has been no compelling evidence suggesting any god(s) or other supernatural being existing in our observable universe.
There is, however, concrete evidence of things like a 4.6-billion year-old Earth, a 13.7-billion-year-old universe, evolution, and general relativity. Science provides the best, most accurate, most predictable, and most realistic explanations for phenomenon we observe. Fairy-tale books that are over 1,000 years old, do not.
Find me a scientific publication that suggests strong evidence that one or multiple gods exist, then I would consider such a possibility.
"Never argue with stupid people. They will drag you down to their level and then beat you with experience."
-Samuel Clemens