Islam had preserved the greek sciences and maths, and continued work on them, but destructive invasions had destroyed libraries and thus texts, and a more conservative sect of islam had begun to influence the muslim regions. Crusades/Mongols, mostly a mongol burning of a library, did the physical destruction, and fear + conservative influence did the intellectual harm.
Then the renaissance happened, and the scientific traditions absorbed by the Persian and Islamic empires ended up returning back to Europe.
I guess, it was just part of the rise and fall that happens to any empire or civilization. The 'golden age' of Islam was over and things were lost.