Let's go back to 2012, when the Windows Phone 8 was the hot new thing. Well, early 2013. When most of the phones on the market were actually WP7 phones with no upgrade option. At all. But hey, it looked so nice. So different. And you remember, Android was quite bad back then. Unless you wanted to buy an expensive high-end phone. Maybe? Well, then there was this option of a reasonably priced, very nice (ex-Nokia design, still some N9 heritage, colorful plastic, you know what I mean) Windows Phone. It was new and exciting. It even had a desktop operating system to go with it. Full of new courageous stuff. Microsoft was suddenly quite cool and hip.
So I got one of those and I was happy with it. I didn't even feel that terrible need for more apps, because there were apps. Not too many, probably, but all I wanted was there. Decent web browser (called Internet Explorer, yeah, that was sooo weird back then), this OneDrive synchronization, good basics. You could read both Twitter and Facebook feeds through an aggregation in the 'People' app. You could even, for some time, do the Facebook messaging thing in the regular Messages app, same one as your SMS. Not that it worked great, but...
...they promised it would, eventually, some day. But it took so long to do a single feature update in form of the WP 8.1. By then, Android moved on, of course.
And Microsoft did as well. They killed the WP 8. By announcing a new version, this Windows 10 wonder. Which isn't here yet, just an endless 'preview version' stream. And it's already so beaten and pointless. There aren't many new features, it doesn't even have some the older version had. All the apps are new, buggy and more boring.
Of course. There is this promise, promise yet again. Write your 'universal' app once and run it both on the phone and desktop. W10 magic. Isn't it great? Alright. No. All the other platforms have it already. If you want to run your iOS app on the OS X, you have to do some development work, but it's not a major deal. You can, if you really want. Nobody really wants. Android now has a runtime with every Chrome browser, installed almost everywhere. Still, little actual demand here. So they broke everything to ship a pointless feature? Probably, kind of. Looks like they did.
What else is there? Lot of brokenness. Like, a lot. All the apps are buggy. And the 3rd party ones didn't see a single update and start to fall apart with all the differences from the WP 8. And of course, why would anyone bother with something, that is going away? They don't.
So I got an Android phone. Again. I just don't care anymore. And hey, this phone is actually good. Things work. I can open the store (well, Play) and there is stuff and I can install it. As opposed to watching the splash screen and having the store crash. Again and again. Which is how it works on Windows. Spotify doesn't miss features and is fast. I can just tap a button and it plays. That's a big deal, compared to the WP. Yes, it is.
And so on. There is still a case for the Windows Phone and I don't think it's going to die. There are still nice and cheap phones sold and I see a lot of them in a tram or bus. But this 'third operating system'? Nope. It's more like a firmware for the feature phone. People will get it if they like the brand (lot of ex-Nokia appeal still) or the model itself, but won't care about getting Windows. Why would they.