I think it is India - mostly Hindus - who seem to reject the Islamic history of India and marginalize it in comparison to the pre-Islamic period. After all, India under Muslim rule was just as Indian as it was under Hindu rule or Buddhist rule etc. Sure, India has the Taj Mahal as a national monument but is that really all the Mughals did for India?
On the other hand, as a Muslim and a Pakistani, I have to see things differently. Indian history remained Indian history even after the Muslim conquests of India. Contrary to what Indians might think, Pakistani history does not begin with Muhammad Bin Qasim, either for me or for Pakistan in general. After all, Pakistan does value and study sites like Harappa and Moenjodaro and others.
Furthermore, we don't view Islamic and pre-Islamic Pakistan and India as insurmountable divide. As Muslims, we believe that Islam has existed since the time of the first human beings, Adam and Eve. God has sent prophets to every people on Earth at various times to teach them versions of Islam relevant to their time and place and situation. Even India had its prophets. They all had the same basic message of worshipping one god alone. And we believe that Muhammad PBUH was the final messenger with the final version of Islam from God that was meant not for a particular time or place or people, but for all times and places and all human beings everywhere. So as a Pakistani, when I look back and I see those ancestors of mine who were Indian Hindus who became Muslims, it was a return back to the original message that an Indian prophet had brought them. We believe that Hinduism, Buddhism, etc are all corrupted and deviated messages that originated from true beliefs from prophets sent by God. So as a Muslim and a Pakistani, I have to say that I can properly own both periods of the history of the land, the pre-Islamic and the Islamic periods. But Indian Hindus I suppose cannot as they view the Islamic period as foreign and alien and not "Indian".