Can't say much about recent history, but the deep archaeological past of India (>~5kya) is difficult to study in part because of the environmental conditions. The heat and humidity make preservation of artifacts over long periods of time nearly impossible, meaning that even though the Gangetic plain was one of the most populated regions on the planet for millennia in the past, there's minimal trace of this civilization left. Ancient tools, shelters, and human remains just decompose in that type of climate rather than being preserved like in the deserts of the Middle East or the cold regions of Northern China and Europe.