Most of the 'invaders' founded dynasties in India and became local over generations. This is no way different than earlier non Muslim invaders like Scythians and Huns. Delhi Sultans and Mughal Emperors were motavated mostly by eartly affairs and they had not much interest to propagate Islam among the vast majority Hindus in the Sub Continent. Otherwise Current India could not have been remaining 85% non Muslims. They employed a lot Hindus in Empire's important administrative and military posts, often commander-in-Chief of the army.
It is true, that some times sporadic atrocities happened aganist Hindus and their temples got destroyed, but those were sporadic, isolated events happened over many centuries and not organied in nature. To understand what organazied religious persecution and forceful conversion look like, you should learn the history of Reconquesta of Spain in 1492 and subsequent treatment of Muslims and Jews there. Not a single Muslims or Jews were allowed to remain in Spain. Either they were killed, expelled or forcefully converted.
Some Muslim invaders did wrong thing like Timur the lame, he massacred 100,000 people in Dehli, but his victims were both Hindus and Muslims. Sultan Mahmud looted Somnath temple. but his motivation was mainly acquiring wealth, not religious. Oppresive Brahmanist gangs in those times made temples the richest places in India by exploiting the masses and hording riches in temples. Those temples became easy and lucrative target for foreign powers who were eager to get wealth.
Most of the conversion to Islam happened in the Sub-Continenet through the influence of Sufi Saints, not through Royal decree. In every Bangladeshi cities there are famous Saints who were very popular and spread Islam through their personality and charsima. The very famous saint in Bangladesh includes Hazrat Shah Jalal in Sylhet, Shah Makhdum in Rajshahi, Bayezid Bostami in Chittagong etc. Khan Jahan Ali was a popular saint in Khulna region of Bangladesh around 1400AD who is still revered by both Muslims and Hindus for his outstanding humanitarian works. He was both a saint and local administrator, he built roads still in use after 600 years! he cleared Sundarban jungle and distributed land among the poor and did many other pro-people works. He was also a great builder, he constructed the famous sixty-dome Mosque which is now a UNESCO World heritage site. Hazrat Shah Jalal and his 360 disciples spread Islam in around Sylhet region of Bangladesh around 1300AD. His influence is still paramount in Sylhet. This is the story repeated over and over again in Bangladesh and I am sure other places in the Sub-Continent where there is a substantial Muslim population.
