For the record: I am a Windows Phone user (using WP 7.5, I have no intention to upgrade) and I actually enjoy the environment. Yes, I am a little bit biased but trust me when I say that I can easily set that aside. I'm a fan, not a fanboy.
I think that Windows Phone ("WP") has plenty of potential to gain a good share on the mobile market. There are plenty of advantages to think of. The simple, blocky, interface may seem a little off at first but once you start using it you'll soon come to appreciate it as well. Especially if you care more about functionality than looks.
But the problem is that Microsoft made a horrendous start, like they always seem to do. WP started out rock solid: hardware manufacturers had to comply to a very specific ruleset in order to call their product "Windows Phone". This gave us users the strong impression that you bought into something for the future, something with a longer time period. Just like Windows itself: I got Windows 7 around 2012 and I tend to use it around its EOL in 2018. That is 6 years worth of Windows 7.
SO we could easily live with the shortcomings of the first devices. It didn't have todo lists? Not to worry: future updates were bound to fix that.
Yeah, and around that time we also learned that Microsoft was ditching their WP7 line entirely and got ready to move onto WP8. Thanks for all the support dear users, now get ready to buy into Windows Phone again if you want to continue to enjoy the full experience.
That may work if you're Android or iPhone (interesting is to note that both environments don't do this: you can run modern version of the OS on older devices if you want to) but not if you're still desperately trying to gain extra market share. You need to attract customers, not piss them off.
Speaking of these other environments... User accessibility is also a big thing. I actually enjoy programming within Microsoft environments like .NET. I enjoy both C# as well as VB (mostly within VBA, but still...). So obviously I was thrilled at the opportunity to "hack" my phone. How can it get more geekier than hooking up your phone to your computer, firing up a free version of Visual Studio and try to get your phone to 'do' something?
I was honestly excited to learn about function calls within Windows which allowed me to control my phone. I really was. But I became horribly disappointed when I learned that the only way to dive into this new hobby of mine was to buy a developers license for E 100,- with Microsoft. That is a lot of money for something you're not even sure you want to dive into. Sure: I knew about the emulator. Did you miss my geek comment above? Anyone can play with an emulator. Where's the fun in that? Messing with my phone which I paid for, that is fun.
And as usual it wasn't until later when Microsoft realized their mistake and ended up providing free access to it. But as always: too little, too late. A lot of real fanatics, some really enthusiastic players, had already moved on. After my previously mentioned disappointment I uninstalled the WP SDK and never looked back. Sure, I know I can pick up the pase again if I wanted to. But the disappointment also made it loose its appeal. And another thing: Microsoft disappointed me once, what guarantees do I have that they won't do so again? Back then that was an issue: I could buy into WP8 and try again. But what guarantees were there that they wouldn't just drop the whole thing again as they have done before?
WP has plenty of potential. But the problem is that Microsoft doesn't know anything about appealing to its customers. They still think that they can dominate the market and that people will follow them no matter what. But times have changed... dramatically.
And until Microsoft changes that mindset then yeah... Then this will probably never come to pass.