In the other agrarian civilizations the human sciences were either unknown or of minor importance. In Africa and the Americas there was nothing. In the Middle East, India, and China there was some history and some political thought, but far less than in the West. Why?
Lack of freedom? Yes, this was important. It is quite different being a court historian, an official chronicler, rather than being an intellectual with a base in an independent institution.
No critical mass? This seems so except in China. In principle, China should have had a critical mass, with a large literate class of government officials. But curiosity about human affairs seems to have been lacking. Also, China was more interested in practical knowledge than theoretical. China was second to none in inventions.
Lack of competition? Maybe this is an additional reason why China was less innovative in the human sciences.