Kirk said a mutually agreed decision was reached by NZR and Robertson for him to step down.
This came after a thorough review completed by Kirk, NZR board member and former All Black hooker Keven Mealamu, and independent reviewer Don Tricker, who was involved in the 2007 post-World Cup review, and who worked with the side during the two subsequent Rugby World Cup wins in 2011 and 2015, over several weeks where around 20 players, senior management, and all coaches were consulted.
There was no 'revolt', Kirk said.
"It's the mature and appropriate listening to players. Players, in the end, are the people who have to deliver on the field first.
"They need to be in an environment and they need to have coaching, and the way in which the environment is managed and set up in a way which helps them perform on the field. I was impressed with the players."
Their feedback was 'thoughtful, balanced, and focused on the team's best interests, with no preconceptions'.
Kirk said the Board’s main concern was with the team's trajectory, a reference to its overall performance, rather than single matches, where inconsistencies, lapses in performance, most notably in third quarters, and in penalty counts.
Kirk said he had a 'great deal of respect for Robertson’.
"He has stepped down on the basis of what he believes, and we believe, is in the best interests of New Zealand rugby, and of the team.
"That's very typical of Scott that he would do what he thought was right and best for the team.
"We thank him very much for that and also pay tribute to the contribution, the more broader contribution he's made to New Zealand rugby over an extended period of time.
"He's an All Black, he's played for the All Blacks and has contributed a tremendous amount through his coaching success, particularly at the Crusaders and the NZ Under-20s as well and a range of other ways. I want to thank him publicly for that and wish him all the best."
Kirk said Robertson had done some good things during his tenure, including introducing a number of young players who had learned the intensity and accuracy required at the Test level.
"There are a lot of strands, a lot of elements to the development of the team, and it's a challenging environment.
"We weren't seeing the trajectory that we wanted and fans will probably share that view that there were things in the way we were playing and ways we were falling short of the excellence that we were looking for that never really got addressed over the year."
NZR will go through the process of appointing a new coach, and the contenders will present plans for how they would approach their coaching.
Kirk said they would seek as many candidates as possible for the world's greatest rugby coaching role.
"We're very hopeful we'll see plenty of highly-qualified candidates."
Watch the full press conference here.
