Answer:
Because the Islamic Empire, during this Golden Age, ruled over such a vast territory, it got in contact with important cultural advances, specially those of the Ancient Greeks and Romans, and those of the Indian Subcontinent.
From these cultures, they took some ideas, developed them under their rule, and spread them back to Europe, effectively serving as a bridge of human knowledge during this time period.
For example, Islamic scholars took Indian numerals, and developed them into the Arabic numerals that we know today (1,2,3,4,5,6,7,8,9,0). They also recovered many works of Ancient Classical philosphers, and brought them back to Europe.
