"Hey, we're a company. We have things. That doesn't mean users use our things, or that developing for said things is going make you money or a userbase. That requires looking at the market and seeing where users are."
They create the supply side. If there is no demand, blindly working in their tools is just a silly mistake. I think it has been plainly demonstrated nothing Windows Phone offers entices the mobile market away from Android en masse at this point.
And part of the reason for the poor app ecosystem is that they've actively discouraged developers from developing for their platform. Heck, there's a huge number Android and iOS apps that are written in C# using Xamarin, and are therefore theoretically very easy to port to Windows Phone, but haven't for reasons as basic as the developers not wanting to upgrade to Windows 8.
If I were Microsoft, I'd give significant $$$ to folks who have created cross-platform app development platforms. Then I can improve the number of Windows Phone apps pretty quickly. I may not get apps optimized for my platform, but at least I'd have something, and then I could offer additional incentives for optimization. That's what Amazon is doing with the Fire phone and developer credits.
Xamarin would be one example, and PhoneGap (or whatever it's called now) can probably be made far nicer and faster. Last year Microsoft did announce a partnership with Corona, but as far as I know nothing has come of it yet in terms of a public release of the SDK: http://coronalabs.com/blog/2013/10/29/windows-phone-8-and-wi...