I have seen many applications related to many domains in all other Operating systems but in the windows store there are very less applications available and that creates a lot of negative impact on the customers phone choice.
Most of app developers think: "The most popular mobile platforms are iOS and Android. So, we will develop our app only for those platforms because there are too few Windows Phone users and we need to save our money
Many young programmers think: "There is too few work for Windows Phone developers. I would better choose another field of work"
If you know XAML and C#, it's easy and fun to create Windows Store and Windows Phone Applications.
If you don't know any of these two, don't worry you can create these applications in HTML, CSS, JS also.
Or you can choose XAMARIN or APACHE CORDOVA to create applications.
You have also another choice - Unity.