Why not Jakati and Tyagi when Ishant and Ohja?

May 4, the Board of Selectors came out with the 15 member squad for India in this T20 Workd cup in England coming this June. I was disappointed with the choice of players. For me 13 was ok! But I felt that Sudeep Tyagi and Shadab Jakati(Chennai Super Kings) deserved a place in the T20 World cup just for the reason that they played exceedingly well and came with results. Tyagi took AB De Villiers for a duck in a crucial match against Delhi and Gibbs for a duck against Deccan. Jakati the spinner took 4 significant wickets against Delhi and Deccan each. On the other hand Ishant Sharma is struggling to prove himself on the line and length though a good pacemen. And Ohja ofcourse has not been that impressive in line with Jakati. I dont know on what basis the selection goes, but as a layman I could spot the two as important for India esp T20.