Why is Kolkata's GDP $150 billion dollars,almost double the GDP of Bangalore?

Hardly double. More like 30%-40%.

This with 60%-70% extra population, a proper port, far better agricultural and hydrological resources, a headstart of nearly 150 years in real terms, as well as the dubious virtues of the “Indian Renaissance” or whatever the phrase is these days.

Calcutta is 'rich' in the way the fat-encrusted wobbling chins of a glutton dying of Diabetic Ketoacidosis is a sign of Health.

The primary reason for Calcutta's riches is that, for two hundred years, the Powers-that-be thatve controlled most of our Holy land of Bharata have persisted in a morally corrupt, economically stunted, philosophical degenerate Colonial System that leeches the wealth of 'defeated' nations to flatten the seats of the High and Mighty.

Fitting, really- considering the kind of human rights-loving Hypocrites who have ruled Bengal all this time.

Bengal, being the centre of Firang campaigns all over the Continent, benefitted from the loot and plunder dragged over the entire Continent. The so-called Bengal Presidency served as the great beast upon which the city of Calcutta sat and swole like a blood-thirsty diseased mosquito. The vast agricultural fields of Orissa were divided among absentee clerk-zamindars in Writers' Building. The sweeping hillsides & meadows of Assam were overrun by notaries & lawyers from Chandernagore. And the less said of what happened in Chhotanagpur, the better.

If anyone thought things would improve after 1947, they were clearly wrong in the head.

The Republic of India is a D.E.M.O.C.R.A.C.Y.

In other words, if you don't have the votes and don't have control of the Gormint- SUCKS to be you.

As the most populated state of the East & the sole link of Mainland to the North-East, Bengal benefitted from Delhi's preferential policies towards it - at the expense of other Eastern and North Eastern states. The Socialist Heroes, when they weren't awarding themselves Bharat Ratnas and wasting Public Wealth on grandiose parades to build up their personality cults, bestowed Bread and Circuses upon the Fortunate and heaped indignities upon the starving Unfortunates.

And here, the capriciousness and malevolence of Bengal's ruling class aided Bengal, albiet unintentionally. With so much public attention across the Nation fixed upon the most recent riot or union strike or lynching at Calcutta, who cares if the Chinese overrun a state or two?

After all- in the words of a noted lover of children, 'that land is worthless; not blade of grass grows there'.

And thus it's natural that the Republic, in its ceaseless attempts to surpass the Raj it has replaced- introduce an even greater drainpipe from the “hinterland” to Calcutta. This was the Freight Equalization Policy.

Neither the guns of Baron Robert Clive nor the ships of Earl Canning struck Oriyas and Biharis and the peoples of the North-East as great a blow as the pen of the great leaders of the Republic of India. For forty years, our lands were raped by the great leaders of Delhi. For forty years, every ingot of iron, every ounce of coal, every single twig that grew and every single flower that bloomed- nothing was ours, but as not which could not sent to the great factories of Calcutta- funded by Delhi 'to compensate for the loss of Dhaka', incubated by Delhi 'to appease the Communists', and coddled by Delhi on account of this glorious concept of “One Man, One Vote”.

Systematically, the Republic punished any who would've set up industries anywhere in the East- save Bengal with its vast ports. Systematically, the Republic subsidized the drain of Eastern metal, the destruction of Eastern forests, the exploitation of Eastern labour. Great Nehru ensured that all roads from Oriya mines ran to Calcutta, not Bhubaneswar. Glorious Indira ensured that Coal from Singhbhum lighted factories in Diamond Harbour and not Ranchi. Heroic Rajiv ensured not one orange could be sold in Guwahati without Writers' Building sucking it dry.

IT policies, One Window Clearances, Road networks…

Ha! They are nonsense! Bangalore would, presumably according to Quora's doyens, be better served in creating a neo-Colonial hinterland to suckle it as ravenous lupine cubs lap the blood from a dying doe's teats!

The prosperity of Calcutta is the prosperity of the Pit- built in the blood and bones of millions of us lesser Children of India- Orissa, Bihar, Assam, Jharkhand, Chattisgarh- labouring under the virtues of “Sustainable Development”, “Freight Equalization”, and “Five Year Plans”. It is the culmination of all that maddens the just, that inflames the valiant, that torments the Dharmic. It is the Chains that have bound this People, that have caked the sinews, cracked the skulls, caked the nerves of the nations of the East whose Aquiline Banners had once shaken the Walls of cities on the Sindhu. Like a gilded harlot, whose allurements cover nothing but the disease-ridden charnel house within, the City struts itself on the sewage-shores of a once-sacred Sea, calling to every Naxalite, Communist, and Malcontent across the Continent- “FEAST”.

Bangaloreans would have to be deluded to emulate this.