[thesuperbigfrog]

1) Poor Timing: They shipped third in a crowded and competitive market where Android and Apple were already established players.

2) Insufficient Apps: they did not get enough developers creating applications for the Windows Phone ecosystem to have a compelling enough platform that was self-sustaining. They even started to build "app bridges" to make it easy to port Android and Apple apps to Windows Phone, but ultimately gave up after a few years of trying with little to show for it.