Why has NSE 'unfair access' issue dragged so long?

A look at key sequence of events in the NSE unfair access issue

Sebi gets three complaints letters in January 2015, August 2015 and October 2015 highlighting flaws in the National Stock Exchange’s (NSE’s) algorithm trading systems. The letters also make allegations of “unfair access” to certain brokers at the exchange's collocation facility. The letter says between 2011 and 2014, the set up at NSE allowed certain brokers (who connected first to the exchange’s system) received data ahead of others and thus were able to react to information before anybody else.   

Following the letters, Sebi sets up a team to do fact finding of the complaints in late 2015. Based on the