That story is enough for a whole collection of books... But one explanation is that China didn't see the need to grow or improve their technology. They could a

That story is enough for a whole collection of books... But one explanation is that China didn't see the need to grow or improve their technology. They could afford to stay stagnant or even suppress technology because they didn't have major threats from nearby states. Whereas if France/Britain/Italy/etc had done the same they would have been conquered by their neighbors.