My perception is that the .NET culture is still much more Microsoft centric and curated and there is less tolerance or interest in technologies that are not endorsed and promoted by Microsoft/Xamarin.
Isn't MSBuild a Microsoft created and owned tech? The NAnt/MSBuild story you cite seems to confirm my belief: the official Microsoft/Oracle had a weak build solution so open source fills the role... With Java, the third party tool achieves predominance because it's just that good. With .NET, the Microsoft tool achieves predominance because it's Microsoft.
When Steve Jobs expresses negativity towards Flash or Blu-Ray, I'm sure there is plenty of disagreement within the members of the team, but it is reasonable that that viewpoint is representative of the team as a whole and the direction they are going in.