There is a certain prominent editor who can vouch that I predicted DVC the movie would flop before I even read this. (He agreed, & I vouch for him, too.) I have only an intuition, but he offered a rationale he picked up somewhere:
Who was it who said, “Imagine this story, where the dead naked public-sex-act guy with the pentagram is the good guy IN GIANT PICTURES instead of in a book. It won’t work.”
The book however, apparently does undermine faith. Survey proves it. At least a boring movie won't send people out to read the original.