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Because it is undiplomatic for foreign heads of state to act unilaterally with regional heads. How do you think the US would react if we did the same kind of maneuvering w. Arnold Schwartzenegger of California? We'd be given a boot by the Federal Government. And the British recognized Modi not because of his superb administrative skill, but because they hope to corner money making opportunities from the state of Gujarat.
It is a scary scenario, especially for freedom of speech and freedom of expression, if Modi should become PM of India. The only thing left to do for a democracy lover would be to don olive green pants and shirts and run the hell away to the Dandakaranya forests.