Have you looked at the Android Play Store lately? Its Facebook, Netflix, Twitter, the McDonalds app (#16 !?!?!) a few other social things, games ... and the rest is total crap.
Why take this ocean of garbage onto a new platform (and at the same time, alienate existing developers who now must compete with Android apps)?
If app popularity obeys power laws (0.005% of all apps make 60% of all app store revenue)[1], seems a better strategy is just to make sure you have the few essential apps necessary, and then provide great tools and encourage developers to write the rest.
> At present there is no motivation for developers to develop for Windows Phone
I've been developing for Android quite some time, and the economics of the platform are not appealing. There have been several articles saying the cost of Android app dev is between 20-30% (minimum) more expensive than iOS[2].
As Windows 10 adoption moves along, it will be more enticing to write a univeral app for that platform and mobile.
[1] http://arc.applause.com/2015/11/11/app-discovery-strategy-an... [2] https://adtmag.com/articles/2015/11/02/android-ios-costs.asp...