Why do we know more about society under the Shang dynasty than we do about society in the Indus River valley?

To answer you question we know more about the Shang dynasty than we do about society in the Indus River because the Shang dynasty is the oldest Chinese dynasty and its existence was supported by archaeological finds also because people would find dragon bones and shells that dated back to the Shang dynasty which also allowed scholars to learn more about them :)