Indus Valley civilization is not a true civilization like Egypt, China, Iraq. It is neither documented nor well understood. Neither does it have any continuity with the people who followed
1. Just because something hasn't been discovered yet doesn't mean it won't be understood one day. The university of Sindh has a entire institute dedicated to the Indus language. And 150 years ago ancient Egypt was just as much a mystery also. More excavations by the British led to more discovery. In Pakistan excavations have been slow.
2. The closest relatives to the Harappan people are literally the modern day ethnic groups of Pakistan.
Harappans = Iranian hunter gatherers + AASI
*this doesn't mean the present day Persian population or the Tamils. None of these groups exist anymore.
Aryan migration led to Aryans + Harappans merging giving rise to Indo Aryans.
Some Indo Aryans interacted with eastern iranic tribes giving rise Indo Iranians.
Hence the modern day population of Pakistan
British didn't name it India.
British named their colony India which they wrongfully gave the entire subcontinent.
Historic India = Indus Valley
Even in the hadith, the Prophet SAW referred to India as Al-Hind.
Hind, Hindhu, Hindhustan all derive from the Sanskrit term Sindhu.
Sindhu = Indus Valley
Avestan Persian and Sanskrit derive from a common Indo European language.
In ancient Persian, S sounding words were pronounced with an H.
Sindhu therefore become Hindhu, from which Hindustan and Hind derive.
During the Greek Persian wars, knowledge was transferred to Greeks about a land called Hindhu.
They took the root hINDhu giving rise to IND, INDOS and eventually onto Latin IND+ia.
All these terms = Indus Valley