Humans were capable of speech long before 3000 BCE, so how come people began developing written language only around that time? Why only among the Near East civilizations?
China and Mesoamerica also independently developed systems of writing, so the premise of your last question is false.
Largely the need for written language came from the need to keep records. The fertile crescent was rapidly urbanizing and with urbanization came trade and commerce. In order to keep track of how many bushels of grain a wealthy person had they began to use writing, and of course it was convenient if everybody used the same system of characters.