It is not that players are not selected from IPL. Spinner Chahel, R.Aswin. Rayudu, Bhumrah, Ravindra Jadeja are all selected after their super show at IPL. However, IPL should not be a perfect platform to judge the potential of a perfect cricketer. IPL is 20-20 format where everything goes fast, the batsman has no time to settle down and totally depend on their shots. It may a perfect entertainment but not a perfect cricket.
The actual character of cricketers can be seen in three days or a five-day game where the bowlers too get the equal opportunities. Where one needs to stand on the pitch with both temperament and class. Anyone one can become a hero in T-20 on their day but becoming hero on test match is not so easy. That is why not every player get selected from IPL but those who have the potential to play a test match.
Have you seen how fast an innings get over nowadays in a test match? The waiting temperament is gone. In the end, I will only say that IPL has damaged more to traditional cricket. Let it be just for entertainment purpose.