They’re taught to regard the Koran this way. It’s a socially conditioned behavior.
I was raised as a Christian, and I was accustomed to hearing the important people in my social circle speak glowingly of the Bible. It was “the Word of God”, the “Holy Scriptures”, the “greatest book ever written”. People seemed to unanimously put it at the top of their favorite books list.
When you grow up hearing this chorus of praise, you don’t dare to disagree. To not feel enraptured about this book would be to betray a flaw in your commitment to the faith (and the whole social support system that the faith represents). So you convince yourself that you feel this way too. If I were to have been perfectly honest with myself even back then, I would have had to admit that I found the Bible to be very poor reading indeed. But I couldn’t afford that kind of honesty. It was socially dangerous.
Now that I have no social reasons to make myself like it, I can barely bring myself to read more than a few lines of the Bible before turning away in complete disinterest. I have tried to read the Koran, and have found that it strikes me the exact same way.
I can fully understand how, if one is told by people that one respects that here in these writings is the repository of absolute truth, one would want very badly to see that this is so. And wanting badly can affect one’s perceptions.