Sorry to break it to you, but .NET has been devouring game programming for years. Unity uses it extensively, XNA was until recently a big choice for indie development, MonoGame is growing, etc...
MonoGame is meant to be an OSS XNA replacement. It's very good for indies with good programming skills. Fez and Bastion were implemented using XNA/MonoGame. If one is more of a game-designer/scripter or is business-oriented then Unity3d is also a good choice.
Completely anecdotal, but I would bet it was due to difficulty getting returns from the program. DirectX itself helps sell licenses of Windows, but XNA not so much due to only impacting indie games.