Congress is arrogant and refuses to talk to BJP. They talk to the left as if they are the only people who matter.
Congress does not recognize the existance of opposition. BJP may be their opposition, but they would have supported the nuclear agreement. But if Sonia and co act as if only the left matters, why should BJP get involved? Some say that for national interest you should give up your ego and rise above it, but if Congress is going to spite you for it, is it fair to expect BJP to play ball?