Earlier quoted context omitted.
Multiple reasons imho: They got a great deal from Microsoft that Google wasn't willing to match, the OS is beautiful, plenty of existing Xaml developers, great platform + language and better tooling than Android or iOS.
Everyone is under the impression that the waters are poisoned or they'd be flocking to the platform. XNA is actually a decent toolkit, and the Visual Studio environment is way better than the Android Eclipse mish-mash. What's preventing uptake is a complete lack of understanding in their market, an inability to take down even weak competition like RIM, and no clue how to leverage their success from the 360 on to a ph…
It's quite obvious that the Windows brand is burned; people hate Windows -- and Microsoft know it better than anyone else!
They had a campaign some time ago where they tried to demonstrate that people actually liked Vista, if only they didn't know it was Vista.
Of course, what it really showed was that people are incredibly prejudiced against the Windows brand.