Uh.. you do know that during the dark ages the Muslim world was having the opposite right? There was a point in time when they were some of the most enlightened people in the world, why and how that changed I don't understand.
It's because this is a completely misunderstood concept... basically a myth. The Muslim "golden age" was only a result of their conquering of what had been western institutions, and in fact resulted in regression, not progression. They suppressed ideas not in line with Islam, and basically took credit (historically speaking) for concepts and creations of previous societies.
THAT is why they failed, and were eventually supplanted as "enlightened" thinkers, because they never had the capacity or willingness to become "enlightened" as a religion.