Why was another index launched even though Tata Group had one index in existence?

Following the launch of the Nifty Tata Group 25 per cent Cap Index by NSE on April 8, a total of four corporate group indices are currently in existence. The other three indices include Nifty Tata Group Index, Nifty Mahindra Group Index and Nifty Aditya Birla Group Index. Nifty Tata Group Index comprises shares of a total of 21 companies, while Nifty Mahindra Group Index and Nifty Aditya Birla Group Index comprises shares of 9 and 8 companies respectively. Auto sector leader Mahindra & Mahindra has 55 percent weightage in the Nifty Mahindra Group index. The weightage of UltraTech Cement in Nifty Aditya Birla Group Index is 40 percent. The base date of all four indices is April 5, 2005 and the base value is 1,000. To be included in any group index, the concerned company must be a member of the group and listed on the NSE. If any group company comes up with an IPO, it is included in the respective group index and after this inclusion, the weightage of the respective index is also reconstituted.