Some reasons:
1. Most Indian families want their kids to become doctors or engineers, computer scientists, or technically proficient. They consider athletics and sports in general to be a waste of time. Similarly, for most Indian families studying majors like history of art and sociology is a waste of time and does not lead anywhere.
2. While it is true that Delhi and surrounding areas are cool or even cold in winter the smog which is almost ever present would not be good to train in.
3. Indian food is delicious but in my humble opinion I don’t think it is the most favorable type of food for athletic performance in that it is very high in calories and fundamentally not healthy. Longevity in Indy is actually quite low and a lot of people die in their late 50s or early 60s from diabetes and heart attacks, even those were vegetarian.
4. Virtually no running culture or people to look up to for kids to emulate in India as far as long-distance running goes. There have been some outliers but they are few and far between. The Indian athletic Federation regularly recruits Russian coaches for the track and field Federation but many athletes cannot withstand the rigors of training under a Russian system coach.
5. Sports is dominated by cricket and kids who have sporting inclinations naturally gravitate towards cricket - it is basically a national obsession. Top class cricketers at least can make money but this is not the case with runners so Indian people will consider running to be a waste of time in the vast majority.
6. In India, money and status are everything, so skinny distance runners do not fit into that mold.