All the players in the current Indian side are either developed by IPL or are a find of IPL. Many posters forget the development aspect which the league offers, Kohli, Rohit, Dhawan are all developed through IPL. By development I mean the confidence a young guy gets when the play alongside the international stars and experienced players. They are all developed through early seasons of IPL.
Also IPL has found talent in the form of Ashwin, Jadeja, Chahar, Kuldeep, Bumrah etc. Indian team has been a reasonably stable team that is why we are not seeing such inflow through IPL, bcz their current players are already performing.
Last season there was a spinner in IPL if I remember correctly Mankhande, I didnt watch a lot of matches but he surely took good amount of wickets. If he was in PSL he would have been selected for the national side straight away bcz our current side is still under construction and we need some players.