We are following the history books which were prepared during British rule. It suited their objective: to eulogy the invading the country and ruling over the majority of Hindus. Many such marauders were fanatics, bigots, and oppressors.
This trend continued even after the independence. Nehru himself found the scheme to suit his anti-Hindu stance. He went ahead and even glorified these despots by naming the roads and structures in their memory ( Aurangazeb road, Tipu for instance )
To glorify these aggressors, the glorious past had to be kept obscure to keep the study of valours by local rules. That is why no one knew Cholas, Pandian’s, Chelas, Vijayanagar, Kakatiyas, and Ahoms. To top it all, Marathas, who virtually ruled significant portion of the subcontinent for 2 centuries, find 3 pages and the greatest Indian icon Chhatrapati Shivaji Maharaj, half a page! in the NCERT history book!
Hopefully, the new regime is trying to overcome this past lacuna. Our nextgen will study real history!