I've written lots of comments, but Windows Phone 7.5 and 8 worked pretty well on low end hardware; much better than Android on similar hardware. If Windows Mobile 10 had continued that trend and delivered on the promise of all WP8 phones being upgradable to WM10, things would be different now.

Microsoft also made some big mistakes IMHO; having a terrible browser and a terrible app marketplace doesn't work: mobile IE was garbage, mobile Edge had a better renderer but worse UX, and they prohibited other browsers at least initialy (Firefox wanted to make an internal port, but were told no thanks). The way they managed APIs for apps led to multiple generations of apps and developers noped out at each stage; WinCE -> WP7 -> WP8 -> WM10 all wanted significant reworking, and WP8.1 wanted a minor reworking. A lot of WinCE apis were available in WP7, but Microsoft wouldn't tell you and wouldn't be happy if you did it. You could run WP7 apps in WP8, but to get new features you had to do the rework and distribute two separate apps. Same for WP8.1, but now you had 3 apps. And again for WM10 ... with the bonus that if you had a WP8 app installed when you upgraded to WM10 there was a 50% chance it wouldn't launch after the upgrade. Apple sometimes did some of this, but major OS upgrades usually applied to all phones, and their users upgrade regularly. Android generally puts backports in the jetpack library so you can build for the newer APIs but still work everywhere.

Of course, Microsoft should have understood the importance of backwards compatibility from their decades of experience on PCs... but they were in full forget about everything mode. :P