The simplest explanation is often the accurate one.
The IAF top brass living in dreamland, coupled with PMO forcing MoD to do all kinds of new age experiments on the most important projects and Finance ministry showing the red flag from a small distance away.
This is the reason. Nothing more nothing less.
Simple simple answer. Incompetence at every level of procurement. If it was not for Parrikar, we would not have even the Tejas. And then we will be playin 7D chess to explain why Rafale and F-16 are the cats whiskers.