First off, even as an atheist I don't feel the need to convert others to atheism. I don't feel that there needs to be any competition between religious faith and atheism, and I think it is wrong to view these numbers as tallies on a score board. So with that said . . .
I sometimes wonder if religious belief fades within communities during times of relative peace and prosperity. As the old saying goes, there are no atheists in fox holes. When you are faced with death, poverty, and strife you may seek out answers in religious faith to a greater degree than you would otherwise.
I think people are also seeing that secularism and atheism isn't going to plunge us into some evil dystopian nightmare. As it turns out, society gets along just fine if people are allowed to live their lives as they see fit, even if their choices may go against Christian theology. Attitudes towards atheism are also changing where atheism is much more acceptable than it once was. In the past, people may not have considered atheism as a viable option because of the stigma attached to it.