The main reason we do not have more information about the Indus Valley Civilization is that archaeologists and historians have been unable to decipher any of the Indus Valley writing. This lack of understanding significantly hinders our ability to interpret their culture, societal structures, and historical context.
While it is true that much research has historically focused on Mesopotamian and Egyptian civilizations, the primary obstacle to gaining more insight into the Indus Valley is the undeciphered script, which limits our knowledge about their administration, trade, beliefs, and day-to-day life. Furthermore, while several cities of the Indus Valley have been discovered, including Harappa and Mohenjo-Daro, the extent of excavations and research has not yet reached the levels seen in other ancient civilizations.