Calcutta should not have remained the capital, as evidenced by the poor state the city is in to this day. Calcutta is a rather useless city, very poor, and not very valuable in any sense of the word. India did the right thing abandoning this city. It's good it has moved on.
In many countries, the capital city was chosen when the nation was in its infancy, before time, war, and commerce had an impact on the business of the nation. In most nations, the city of primary economic importance is not the capital city, and this discrepancy can be very inconvenient. When nations change their capital cities, as India did, usually it is a response to political pressure, and doesn't have much bearing on anything else.