I think this is key:
Most people just go with the flow (do what others around them do), without any critical assessment.
I was watching "The Root of All Evil?" by Richard Dawkins the other day and he made a poignant point. The passage of time tends to make things that are not truth truth. Just as long as enough people start saying that it is true, it becomes true and the general populous excepts it as truth. This must be so with the Bible. At its inception, it was not a widely held belief that the Bible was the word of God. There weren't many Christians to begin with. But with the passage of time, those who saw the Bible as just another book died off, and the concept of the Bible as a holy book was codified.