Didn't the problems start even before that? Windows 7 phone was the first new phone platform from Microsoft and was widely regarded as pretty good by the pundit

Didn't the problems start even before that? Windows 7 phone was the first new phone platform from Microsoft and was widely regarded as pretty good by the pundits. It had a whole new set of APIs though compared to Win32 (as could be expected), based on a Silverlight-like platform IIRC. Then Microsoft changed all of the APIs again for phone 8 as you outlined. That really scared off a lot of developers I think. Who would be willing to code for something so unstable? 2 new sets of APIs in as many years, with no kind of overlap or migration plan. All these changes had their reasoned explanations back in the day: the install base was small so it didn't have much impact and they were removing cruft each time, but with hindsight it was a really bad way to go about creating a healthy ecosystem.