Why do the central states of India generally have lower Human Development Indexes?

HDI (meaning): The HDI was created to emphasize that people and their capabilities should be the ultimate criteria for assessing the development of a country, not economic growth alone. (more info)

I am seeing this graph on Wikipedia which gives the HDI of each state in India:

Why is it that the states in the middle are generally less developed? Is there some general reason for this?