This video makes a number of points, but one of the most important is toward the end, where it describes the disgusting way that religious groups treat others:
Irregardless of whether gods do or do not exist, this disgusting behavior would naturally cause some people to reject religion. Combine it with the fact that there is no evidence that any god exists, and you understand why so many people reject religion.
The strange question is this: why do so many people accept religion, despite the disgusting behavior and the lack of evidence? Another question: why do many who believe in gods then fall into such disgusting behaviors?