Aryans, Iranians and IVC

So as far as I understand, the people at IVC itself were a mix of South asian hunter gatherers and Iranian Neolithic farmers from the zagros mountains. Why is so little known of these farmers? On that note we know that the Aryans came at a later stage but was ivc already in collapse or did they come before and mingle? But, the rakhigarhi sample lacks the steppe dna? Then they mixed with the north and South Indian people forming ASI and ANI. So, was it multiple stages of migration? From linguistics it seems that IVC could have been proto Dravidian or one of the languages anyway. Did these aryans settle in the gangetic plains? (If rigveda is to be considered a snapshot of vedic civilization)