Dhoni didn't win any ODI series against a Top 8 from West Indies October 2014 to New Zealand October 2016. The BCCI's silence on Dhoni not winning anything then was baffling. One struggles to remember captains of good teams not winning for for 2 years and still staying put in the face of new talent.
In between Kohli blanked Sri Lanka 5-0 in an ODI series. Maybe finally after winning with the Kiwis, Dhoni must have decided to make his announcement on a high.