Apple has been selling roughly ~19M Mac per year since 2012, and its new user to Mac has also been steady at ~50%. Apple has had 60M Mac user in 2012 announced in WWDC, and they has been nearing 100M since early 2017. I assume that actual number is larger than 90M at the time, so after nearly 20 Months, ~20M New Mac Users on board, it manage to add a total ~10M Active Install Base.
That is surprising for me, as I was expecting ~110M+ Mac User already, others analysts like Benedict Evans and Asymco put those number past ~120M. So for every 2 new Mac Users, there is one leaving.
I hardly call that good news by Apple Standard. And this high churn rate happens after early 2017. From 2012 to 2016-17, there is 4 / 5 New users for every 1 leaving the Mac Ecosystem.
The timing actually align with their sudden Interviews with Apple journalist on Mac, Mac Pro, and the release of iMac Pro.
And judging from these numbers, I would bet the release of MacBook Pro, iMac Pro and MacBook didn't restore the faith of its Mac users. Apple didn't care about its Mac lineup, this new MacBook Air as well as Mac mini were likely reaction to this churn, much like the iMac Pro.
Or may be, the timing has something to do with their New Keyboard Design, which they introduce to MacBook in 2015 and Pro in 2016, and they managed to fit that in this New MacBook Air.