I apologise if I hurt any die hard Windows Phone fans here, but I have a list of reasons why I believe Windows Phone doesn't take off and some suggestions to go along with them as we'll.
Windows Phone is a bit odd of an OS. Android is often described as a complicated but highly customisable and functional software whereas iOS is described as a much simpler phone that just works.
Windows Phone is nor as easy to use as iOS, nor as functional as some other OSes out there it has nothing going for it.
But...this could be used for marketing to show what Windows Phone is truly good at - providing a balance between simplicity, beauty and customisation but I have yet to see this sort of thing advertised(they have mentioned it in a few YouTube videos though).
Moving onwards and elaborating on the same point, Windows Phone or at least part of it has revolved around photography and I'll admit that it did a much better job than Android for as long as I can remember. But sadly they've fallen short there as well, with iOS taking the lead again with arguably the best camera API out there that is used to create amazing apps like Instagram Hyperlapse.
And then once you overcome those shortcomings you'll be faced with a massive shortage of applications, primarily quality gaming titles. And that's not all...even if you find your necessary apps they'll usually be months behind their iOS and Android counterparts.
Once you've come ahead of the apps and games, then there is the social aspect, the likely scenario is that most of your friends own either an Android or iOS device and you'll feel left out or even ridiculed for having a Windows Phone.
Plus Microsoft's services aren't offered in many countries, case in point Cortana and HERE Maps(I'm sure there are others) and you can't use Google services either.
Linus Sebastian, arguably one of the funniest and most well educated reviewers also conveys his thoughts about Windows Phone in this video:
http://youtu.be/c3AgcltUM9s
And lastly Windows Phone is still somewhat playing catch up with Android and iOS, lacking quite a lot of features that the competition has.
I'm sure there are aspects Windows Phone does better, the cameras is one things, but to make a phone or OS sell well you need to excel in most things not just a few.
This is what I believe, I have more reasons but I'm sure no one would want to read a much longer post. Again, I can be wrong but this is what I think having used Windows Phone for some time.