Even if C# would be the most technical superior language ever made with every feature you could think of, a lot of developers still don't like it because:
- C# smells corporate, being used in many large scale business application.
- C# is developed by Microsoft, a billion dollar company itself
- The .NET platform is only partial open source
So facts don't matter much, it's about smell :)
C# is _guided_ by Microsoft. You can join in on the language design if you want[1].
The .NET platform is now completely open source[2]. The compiler (Roslyn), tooling (cli), the runtime (coreclr), and the standard library (corefx) are all listed there, all under the Apache 2.0 license.
What's not open source?
[1] https://github.com/dotnet/csharplang [2] https://github.com/dotnet/