You’re forgetting that they had a good market position with Windows Mobile. They saw off Palm and were competing with Symbian and RIM. Then they rebooted with Windows phone and again with Windows phone 7 and again with Windows phone 8 and again with Windows phone 10. Each generation incompatible with the last. Sometimes even known in advance, e.g The 8-10 transition leaving Osborned devices on sale for nearly a year Meantime Android was available ‘free’ to manufacturers, compatibility was maintained between operating system versions and across manufacturers. Customisation was a big thing for OEMs - look at HTC and Samsung on Android. Every Windows phone had to look IDENTICAL on screen by order of Microsoft.

Microsoft did it to themselves with mobile. Ballmer era MS thought they could ‘bulldoze the market’ like the early PC era again but that didn’t work when they had to actually compete.