Only truth makes a difference. But truth may be useless if it is useless truth, I mean truth that we cannot use. If you cannot spend your gold in your pocket you can’t be rich. Knowledge that we cannot use will not make us wise. So what happened to that knowledge that Muslims already have?
Another thing, most people in general have an aversion to intellectual labor. Most people would be content with what they know than would take a little more trouble to go beyond it. Beyond a certain point we reach our level of incompetence in terms of our knowledge, and thus action.
Knowledge of divine is knowledge of fact. We only unfold it because it already exists. We cannot create it nor we can enhance this knowledge. But I agree with you, we only enhance ourselves within the boundary of this knowledge that we can posses. Worldly knowledge is a knowledge of consequence, we experiment and we understand divine knowledge through its pay back.