What about the plain old "lack of talent" theory? We all assume our players to be super talented based on some good U-19 team performance. But none of our U-19 teams had standout individual performers. Our U-19 success has been mostly result of good teamwork. We never had someone like Shikhar Dhawan or Tim Southee in our U-19 teams.
India U-19 vs BD U-19 in 2004 U-19 World Cup, Dhaka