- licensing
- failure to attract app developers
- lack of Google services like Google maps, YouTube, gmail.
- botched Windows 8 which led to an unjustified bad image of WP
- startup developers did not trust Microsoft based on its past
Everything from this article:
It sounds plausible. I never had a Windows phone. I do not see myself enjoying it. But I think it would have been a very nice alternative especially in comparison to the Android of today.