It started with windows phone 8 and the Metro UI. Bad Idea. The UI was too far away from Android/iPhone to be easily ported and adding corporate design to it was hard as it was too different. Silverlight and XAML was okay for the time.
Then came windows 8.1 and windows desktop 8 which was universally hated. The whole fullscreen apps debacle was just horrible and all the unnecessary restrictions on store apps for desktop made no one ever consider porting their desktop app to a store app. The whole phone and desktop app in one was a joke aswell since it was (and still is!) horrible implemented. Did I mention they broke compatibility from 8.1 to phone 8? I didn't even bother starting all over again for windows 8.1 i just straight up skipped it.
Then windows 10 came and it finally looked like the UWP Plattform might do the trick. Well nope. The SDK is garbage. Scaling from phone to desktop is hidiously bad and afaik still not solved. The Live-Tiles got even worse since you couldn't programm them like the windows 8 ones. Just a whole mess. Couple that with the hillariously bad store interface (backend aswell as frontend) and 0 User engagement and it was bound to fail (as will all UWP apps)
You guys build a, I'm sorry to say but after 3 years of frustration it's fair to say, half-baked half-assed phone plattform that at no point had even a single feature that wasn't available better on iOS and Android, restricted the developers unecessarily, broke compatibility once a year requiring a complete rewrite and frankly build a product that only microsoft liked but was universally hated by their users.
It's a story of too little too late and a whole lot of arrogance on microsofts side.
Oh and don't even get me started on microsoft completely ignoring the european market where they actually got up to 15% marketshare of new devices sold for a while.