That's because once US accepts India's position, other countries will follow and India gets diplomatic advantage of getting recognition of a nuclear state. Once this happens other countries will start suppliing fuel to India as well. But this is irreversible process. They won't withdraw supplies just because US thinks otherwise. They will only consider their own position. So, India has to only make sure it doesn't do something that's completely unacceptable to entire world like passing the technology to a rogue state.
