I guess because atheists do not have a sense of a religious. You know religion is a bond a person with his god. should you (atheists) believe is that every life is a journey toward us into the next life. you believe about life after in the world?
It is impossible for an atheist to believe in life after death or rebirth because these ideas are opposed to humanist dogma and all atheists are humanists since what else could they be?. Since there is so much evidence of life after death, the burden of proof has shifted to the skeptics, they fail to offer a serious scientific explanation to justify humanism.
Researchers van Lommel and French wrote in New Scientist that if there was a documented case of perception and memory formation during brain death then this would suggest that the brain does not generate consciousness. Such a case was provided in the later AWARE study and other cases also have good documentation; there are many other lines of evidence that are very hard to explain without the survival hypothesis, even though it is a nonphysical explanation, it is the only one that explains the hard data and mountains of anecdotal evidence. It has been proven by rigorous science and the same can be said for the Orch OR theory of quantum consciousness.