Windows Phone was late and crappy. It still is crappy. Devs don't want to develop for the platform no matter what MS does now. How can they get the devs back? Universal Apps is Microsoft's way but I am not too sure if that is what devs want. Microsoft are still desperately trying to push one app for mobiles, tablets and traditional computers. I like the idea in theory but then again communism sounds good in theory. Really though we don't have the hardware to fully realise that yet and I don't think we will for the next few years. Personally I prefer how Apple are doing things with keeping computers and mobile/tablet (touch devices basically) separate. Having said that I don't really like how Apple does things a lot of the time. I am a Windows computer and iOS phone user. My phone is a device to get work done so the closed environment isn't a big deal whereas on my computer I want more control. Android is good but until recently it wasn't what I really wanted and now I am too deep in the iOS world to switch my phone to an Android. I think the problem MS has is people don't want to move to Windows Phone. There is nothing WP does that I can't do on iOS or Android.
There is a saying about "every other OS release" of Windows. You can wager with confidence on the accuracy of that heuristic.