because India said it did not need help from Russia.  India can produce all the needed tecnologies for the PAK FA itself. I am not sure how true this claim is, but here is the story.

.Russia and India Had Big Plans to Build a Stealth Fighter. So What Happened?

http://nationalinterest.org/blog/the-buzz/russia-india-had-big-plans-build-stealth-fighter-so-what-26346