The simple fact of the matter is that they can't admit that anything may be wrong or metaphorical unless it fits their world view. Changing anybody's view of the universe, religious or otherwise, is not a simple task. People often go for large portions of their life thinking that they understand what they need to understand, and a number of religions (most prominently the Abrahamic ones that compose about 54% of the entire planet) are very vested in the idea that their holy book is the word of God Himself.
That said, humans are extremely good when it comes to cognitive dissonance and self-delusion (notice how I don't say "the religious are..."; the same flaws exist in atheists, agnostics, Buddhists, and people of every stripe, with religion merely being the most apparent source due to its prominence and especially massive logical issues). Modern values and knowledge have changed massively since the Bible and Koran were first written, and people need to figure out how to deal with that without admitting that everything that they've based their world view and lifestyle on is fallible. Religion holds a much weaker grip on society than it did in the past, and people can freely interpret the Bible however they want. This is how you get the cognitive dissonance of a person who eats shellfish and wears clothing of different materials while claiming that the Bible is true and infallible and hating homosexuals and anyone who's not Catholic, or those who love gays (or even ARE gay) and admit that parts of the Bible are metaphorical or no longer applicable to modern society or even outright false, but cling to the portions that they personally want to believe in.
Actually, Creationism isn't quite as prominent as it used to be. Science and secular life have gained a much greater foothold in modern society. Really, only people who are downright backwards continue to teach plain Creationism or hatred of science. Most modern folk of the Western world are content to stick with Intelligent Design, as it lets them more easily mesh with scientific advancement and an intelligent and logical viewpoint without having to give up their gods.
In the end, religion is comforting. People want to believe that there's an omnipotent, omniscient father figure who watches over everyone and sometimes reaches down to help. They especially want to believe that there's something after death, that life doesn't just stop. Believing in religion, even if it means believing in something that makes no sense or being self-contradictory and resorting to denial and shouting sermons when your logic is turned back on you or has its flaws pointed out, is natural for humanity. It takes more effort and bravery to admit that God and Heaven may not exist than to believe in eternal happiness.