The Scottish Rugby Union last week announced Johnson was taking on the new role to oversee the development of the game and national teams. Johnson on Tuesday named his last squad, for the four-team tournament in South Africa next month, and will make way for a new head coach after their return.
Johnson, who named nine uncapped players in his squad, told STV: "It was a decision I made. There were two jobs out there and I could have taken both - I chose this one because I felt it suited me best. It suited where I am in my life."
The Australian has been involved in the selection process for his successor and will continue to have a major input into the national team, but his desire to instigate lasting, meaningful improvement led him to pick the upstairs role.
He added: "It allowed me to still coach in the team. That was important - I didn't want to walk away from the team. But I like doing the other stuff as well. I'm here with just my wife and I like working and I like meeting people. When you are just the head coach, for a long time of the year there is a lot of down time.
"I like to get my hands dirty and get into things. I'd have loved to have done both but it is practically impossible. So I had to have a choice. This is a really happy medium for me. And hopefully I can make a valuable contribution to Scotland that lives far beyond I go."
With Sean Maitland, Richie Gray and Stuart Hogg on British and Irish Lions duty this summer, Johnson was restricted in his choices for the tournament, which also features Italy and Samoa as well as the hosts.
But Johnson was disappointed he was not further limited after Scotland's third-placed finish in the 6 Nations.
"Selection is such a personal thing, so I'm not going to criticise someone else's opinion," he said. "I thought our performances merited a couple more but when you become a coach you usually favour people you know and have worked with.
"Yes, you were disappointed for the effort the boys put in and how you felt they performed. But you've got to take the knocks and not hide and if we weren't deemed ready to take that mantle, well it's time we showed people that we can."
- Sports & Recreation