The desktop market is mature, Microsoft bought into the hype that the desktop is dead. Mature market is not the same as dead by a long shot. The traditional desktop (and laptop) PC is alive and well, with something like a billion of them in use and they are not going away any time soon. What has changed is the technology has matured so users are upgrading less frequently than ever and the casual users who never really needed a full PC in the first place can now get by with mobile devices. Microsoft missed the boat with mobile, they arrived to that party almost 10 years too late which is an absolute eternity in tech then tried to play catch up with predictable results. Android and iOS were firmly dominant with Blackberry a distant third by the time MS even took the market seriously, by which point it was hopeless.
They threw Windows under the bus in a desperate effort to use it to jump start their mobile platform but that failed, Windows Mobile is dead yet for some reason they continue on the trajectory of "universal" apps that have no reason to exist without a robust mobile platform. They have failed to grasp that "legacy" Windows software and familiarity is nearly the entire reason most people use Windows, succeed in killing that off and Windows has no reason to exist.
Now it seems what they've done with 10 is made one final last ditch effort, sacrificing what is left of Windows trying to get people using their services and app store. One of the problems there is that the services are not needed by a great many of us and the apps are almost universally garbage. I do not use a single default Microsoft app on any Windows machine, for every last one of them there is a 3rd party product that is superior. When I had Win10 at work I found it incredibly frustrating that it kept changing my settings away from the software that I had carefully selected and deliberately installed, back to the crappy default garbage they wanted me to use.