Throughout the existence of mankind, there have been nearly 10,000 gods that people have believed in.
Today, atheists and true-believers agree on 99.9% of all the gods that have ever been believed in and worshipped as being false and non-existent. Accordingly, as compared to modern-day believers in a current god, atheists simply just "go one god further" ... as is often said.
And if there were only one religion, with one god, and one “holy” book, it would be a lot easier to believe. But since there have been thousands of gods across hundreds of cultures and across many millennia, it is impossible for them all to be true. So the best conclusion, at least for me, is that they are all false.