Question

Why do you think we know more about Mesopotamia and egypt than about the indus river

Answer 1

While the indus river valley civilization DID have written language, we don't know how to read it. 

In Egypt's case, we used the Rosetta Stone to decipher there language. Same with Mesopotamia. We know more about Egypt and Mesopotamia because we gained a lot of insight by reading the texts from that time.