Because the theory of evolution itself evolved into far more than a simple scientific theory. It hemorrhaged into an entire mindset for the course of humanity. It itself became a sort of religion that viewed mankind as having a sort of Manifest Destiny.
Evolution is not simply contrary to biblical literalism. It "imagines" a world where humans can 'evolve' into something more than they already are, even though there is no evidence that civilized society has grown more intelligent, peaceful, understanding, wise, healthy, or strong than it was thousands and thousands of years ago.
THIS is the problem that Christians have with evolution. It turns mankind into a kind of god. It's not that we simply cling to our bibles (which have done MUCH more to help us along in life than SCIENCE ever has
) but evolution literally scares the bejeezus out of people like me, because it gives these crackpot geneticists who want to clone babies and splice genes justification for their 'Frankensteins' (perfect book to read, btw).
I'm not discounting the EVIDENCE of evolution, I just think that the EVIDENCE might actually point to a more believable conclusion.