I've rolled this around a bit and have come down on the side that there are two factors at work.
1. Just plain Microsoft Hate. Couple of times someones asked me about what language to use for some GUI that messes with a database and does some other thing, running on Windows and 'maybe Linux' I tell them that C#/.net was made for that kind of thing. And they recoil in horror as if they just realized that I'm Satan. Then they go off and mess around with QT/C++ for a week before giving up.
2. C# has good inter-op with C/C++ libraries. So if there is an open source widget in C/C++ you need you can usually just build it as a dll with some wrapper magic and reference those in your project.
1. Just plain Microsoft Hate. Couple of times someones asked me about what language to use for some GUI that messes with a database and does some other thing, running on Windows and 'maybe Linux' I tell them that C#/.net was made for that kind of thing. And they recoil in horror as if they just realized that I'm Satan. Then they go off and mess around with QT/C++ for a week before giving up.
2. C# has good inter-op with C/C++ libraries. So if there is an open source widget in C/C++ you need you can usually just build it as a dll with some wrapper magic and reference those in your project.