Microsoft execs had their heads buried too deep in their own asses to be able to understand what was needed at the time.
They pushed a platform (Windows phone) that lacked interesting features out of the box, lacked cloud services integration to fill the gap left by the lacking base features, and required Windows as a development platform (and, iirc, C# as well?). It didn't even have any particular windows-ecosystem speciality: no special exchange integration, no special windows pc integration, nothing. Microsoft could have exploited the same reasons they exploited with Azure, Office365 and the general enterprise: microsoft phones should just integrates perfectly with other microsoft stuff. It could have been the no-brainer choice: we use ActiveDirectory and Office365 as a suite, we'll get a Windows Phones as everything just works immediately. No, nobody had thought of that.
The value proposition was just not there.
So basically another walled garden, but dumber. And the hardware didn't have anything special to make it "worth".