People who ride motorcycles have a much lower incidence of cancer than the standard population. This is actually a fact that is important for insurance companies because of how they charge for coverage. But, motorcycle riding neither cures nor prevents cancer, what is does is kill the people who are doing it before they can develop cancer. Enough people die in motorcycle crashes or from motorcycle related injuries that there simply aren’t as many around to get cancer.
I generally think it is the same thing with atheism and quality of life. It isn’t that atheists do better, but rather that people who are doing better don’t need religion as much and so are pre-disposed towards atheism. Eschatology has very little appeal to those who are happy now.