How can an atheist possibly make sense of a world in which the vast majority of people adhere to a religious tradition? If atheism is correct and at the basis of all these religions lie mistaken facts and historical inaccuracies- for example that Jesus was risen from the dead, that Muhammad was visited by an angel, etc.- then the majority of humans who have ever existed have based their actions and beliefs upon a lie.
Everybody, not just an atheist, has to make sense of a world in which billions of people have false religious beliefs. That simply must be the case, considering that there are lots of different religions, and they contradict one another. Billions of Christians are wrong about the divinity of Jesus OR billions of Jews, Muslims, Hindus, and Buddhists are wrong about the non-divinity of Jesus. No matter what your own religious beliefs, you've got to admit that in the domain of religion, people are especially fallible. Why is that? We could entertain lots of different theories, but atheists don't have the explanatory burden here. Everyone does.