Why was the information from the Muslim Golden Age not yet been fully discovered

During the 13th century the Mongol Empire conquered most of the Eurasian land mass, including China in the east and much of the old Islamic caliphate. The destruction of Baghdad and the House of Wisdom by Hulagu Khan in 1258 has been seen by some as the end of the Islamic Golden age. (basically because of the Mongol invasions information was destroyed and lost)