Windows Phone lack of success is simply the fault of not getting phone out to the pubic. Thier marketing department blows.
When windows phone first came out MS should have flooded the market wiith low cost or free with a contrat phones to build a base, that would be willing to stay.
The OS is nice, and with some tweeks here at there it could easily rival android, and possilby i0S in time.
That sounds like "logical" but to be honest, that's not the reason, at least from my own perspective. Over the years people have grown tired of the Windows monopoly and wanted choice. Either at work or home you were basically forced to use Windows if you wanted to get along in the computing world.
It's not that way anymore. That's one of the reasons Blackberry was so successful in the business world. It wasn't Windows. But then Blackberry had a monopoly. Then Apple and Google released their OS's and now people have choice. Windows Phone and the Surface aren't very successful because people now have choice and are no longer being forced, with the exception of some business entities.
This is the same issue with the Xbox One vs. the Playstation 4. People have grown tired of Microsoft and they can't catch up to Sony with the Playstation 4.