Thing is, Silverlight and Windows Phone 7 were already two steps that made developers go WTF. There was WPF, hot off the press and obviously very promising (but also obviously requiring a lot of polish; I don't think it was truly ready until .NET 4). And then instead of actually, you know, polishing that, like we did with WinForms, there was suddenly that new Silverlight thing, which was obviously very similar but not quite. That was when third party devs first started balking, but it really went into high gear when Windows Phone 7 guys said that their XAML will be yet another different thing. By the time we got to Win8, the developers for the platform were already allergic to all this nonsense. So I don't think it would have helped much to support WP7 apps (although it certainly wouldn't have hurt!).