Largely because accepting the accuracy - at some level, whether literal or not - is not an act of reason, but one of faith. It's a feeling that it's true rather than a conclusion, and then - as we are all wont to do - the reason follows trying to justify the feelings.
We're all guilty of confirmation bias, of seeking conclusions and explanations that suit our preconceptions, that's human nature it seems. I think it takes a huge capacity for cognitive dissonance to believe that the Revelation is literally true, but I'm guessing that the majority of Christians think of it as some sort of allegory?
O.