Of the three early civilizations situated in Near East and South Asia, the Indus Valley Civilization seems to be the only one whose language we haven't been able to decipher yet. Is it because enough resources have not been dedicated to the effort? Or are there other factors involved?
Not to preclude further answers, but I wrote about this in Why haven't we deciphered Indus Valley Civilization script yet?
Proto-Elamite and Linear Elamite, writing systems from Bronze Age Iran, have not been deciphered for the same reasons.