Dhoni Believed In Giving The Players A Complete Chance.

 In Indian cricket, the captaincy has not changed much in the last 15 years.  After Rahul Dravid stepped down as captain in 2007, Mahendra Singh Dhoni took the lead in ODIs.  He was already made the captain in T20.  The senior players refused to play in the T20 World Cup.  Then the youth team led by Dhoni became the winner.

 He became a regular Test captain after Anil Kumble retired in 2008.  The Indian team then became the number one team in the world in Tests. Moreover, the team won the One-Day Cricket World Cup in 2011 after 28 years.  Kohli captained India in Tests in late 2014 and ODIs and T20s in early 2017. 

Dhoni's only goal was to win the World Cup, for which he made tough decisions

Dhoni was a confident captain.  He believed in giving the players a complete chance.  He wanted the players to get 60-80 matches before going to the 2011 World Cup.  He had experienced and senior players like Sachin, Yuvraj, Sehwag, Zaheer, and Harbhajan.  He also gave a chance to young Kohli, Rohit.

In the end, only Kohli made it to the World Cup squad.  There were also seniors like Laxman and Dravid in the Tests.  Dhoni, including Rohit-Kohli, has young players like Raina, Pathan brothers, Sreesanth.  Dhoni handled the ego of senior players as well as the youth.  He showed confidence in the child despite his failure. 

He took a tough decision for the same reason and dropped names like Ganguly and Dravid from the ODI team.  His only goal was to win the World Cup.  But then the team's performance deteriorated.

Senior players are getting older.  

The team won the Champions Trophy in 2013 but has not won a major trophy since.  Dhoni's biggest problem was that the careers of the senior players were coming to an end almost simultaneously.  Kohli was the most critical player on the team at that time.  Kohli's graph was steadily rising, and the team was not performing well in the Tests.  Dhoni retired from Tests in late 2014.

Kohli prepared a fast bowling attack but gradually walked away from the team.

Kohli captained the Test side in the 2014-15 tour of Australia.  His views were different from Dhonis.  He believed in aggression and brought fast bowlers into the team.  He had success, but gradually Kohli became a little different from the rest of the group.