The answer lies in the geographical interconnectedness and proximity of ancient peoples. For example, the gap between say Egypt, Kush, Carthage and then the Peoples of Sub Saharan Africa were so large that constant trade/communication was very sparse if non existent. The evolution of Ancient civilizations in the Middle East, The Balkans and Mediterranean began and grew so prolifically because of a sharing of Ideas and Technology. The conquests of Alexander the Great helped Western and Eastern sciences and philosophies to flourish. The Roman Empire also helped with the growth of Western Civilization because of its diverse populations all contributing their traditions and sciences. Remote areas such as Greenland, Northern Scandinavia,New Zealand and Siberia were also devoid of major literary and architectural works until they came into contact with other more established civilizations.