And I know, is about proprietary folks that are taking here, right?
I work(ed) in OSS, with .Net and yes, is possible. Is not as major project that you may think, but it give the very same thing you asked for: CAD software. It does not work for Linux and I know that no one worked hard enough to port it for Linux, but the core code could theoretically once work on Linux.
In comparison, there are a lot of reasons why a C# platform would bring advantages, you may heard about them, one of them is the GC. You may like Java more, and is fine about it. You may like type inference (yes, I know is a part of C++ 11), reflection, and so on. And yes, maybe the revision C++ 2021 would bring all these features in C++, and you will wait 5 more years to be supported by all mainstream compilers before writing code with Linq.
The combined percents of users of first 10 languages, comparing managed (with a virtual machine or a runtime, different than libStdC++ or native) against native ones, you will see that managed languages are more used (by a small margin) in todays software.
C# as language, after Java is the second most popular language using a virtual machine, doesn't seem to you that it is used almost everywhere, or at least is fairly useful for normal people?