To all Atheists . . . Give me a simple answer as to why you all don't believe in the Gospel.?

please don't answer like : it's a bunch of B.S., or it's just a fairy tale or story or a cult or anything of the like. I'm a christian and could give you a simple and straightforward answer about what I believe. I just want to see if there is a simple straightforward answer that you could give me about what you don't believe and why.