I'll bite - what's the "result" of violating a "no first use of nuclear weapons" statement?
There are two cases. In one case, you got nuked back. In the other, the folks that you nuked aren't in much of a position to do anything, having been nuked and all.
What is the "result" in both cases? (If said result requires someone doing something, who is that said someone and why/how are they going to act against an entity that has used nukes recently?)
The problem follows after, when India can no longer convince America, Russia, or China that they can be trusted with nuclear weapons.
Economic sanctions would be devastating. India has limited fossil fuels and as of now a not yet fully indigenous defence industry. Being irresponsible nuclear users means all major powers will cut them off because they're a danger to all.
It isn't even clear that other world powers will settle for isolation. They may well require disarmament.
But this time, things changed. Public get to know what has been happening to their country since last 75 years.