I think it could be because there is no solid definition for what a god would even be, so everyone has their own definition and interpretation of things. Meanwhile in atheism, it's hard to mess up a definition of "there is nothing there." Personally, I would find it alarming if I believed in something that had zero consistency from person to person, meaning there can be no aggregate opinion. It's also far simpler to believe in nothing, as occam's razor is a very awesome and true tool.