Likely a reference to this view of the OS war: https://en.wikipedia.org/wiki/Usage_share_of_operating_syste...

Android is first by a large margin. iOS almost outnumbers Windows as well.

Microsoft post iPhone needs to prove that it's worth using a desktop at all, not that they deserve to have the highest share of desktop users. Stopping the bleeding inflicted by Macs, which sync so well with iOS, is part of that.