The most accurate response to why we do not have more information about the Indus Valley civilization is:
B. Archaeologists and historians have been unable to decipher any of the Indus Valley writing.
This inability to understand their written language significantly limits our knowledge of their social, cultural, and economic systems, as well as their historical events. While there have been discoveries of multiple sites within the Indus Valley civilization (contrary to what option D suggests), the lack of deciphered texts is a critical barrier to gaining deeper insights into this ancient civilization.