Why Kolkata is lacking behind in the startup revolution?

Recently, flipkart released its data of shopping patterns and other informations such as which city had most numbers of orders etc.
One thing that struck me is that Kolkata was not in the list of most numbers of orders. Even in the Top 5 cities, 3 of the metropolitan cities I.e. Delhi, Mumbai & Chennai held positions. But kolkata was not in the list.
In a post of YourStory, the Top 5 cities for startups also didn't featured Kolkata. Having a dedicated sector for Information Technology, the SectorV, Kolkata still lacks the startup revolution. The potential of entrepreneurs in Kolkata is still unexplored. 
Being a undergraduate student, with interest in startups,  I wonder why isn't there any name from Kolkata which has turned into an unicorn company like flipkart or snapdeal. Many of big incubation and venture capital firms haven't arrived to explore Kolkata.
I hope the scenario changes in forthcoming years. And big players emerge from the city of Joy.