You have now shifted into claiming that your issue is that the licenses Microsoft released their code under were insufficiently permissive. I could argue against this, because it's at best misleading -- different code was released under different licenses. You can see an archive of one of the CLI releases [1] with the license it came with. Or this [2] is a blog from the Mono founder expressing thanks for Microsoft and ECMA members releasing code under open source licenses. That blog was from the huge 2.0 release, in 2008.
But ultimately that feels like a red herring, even if a fun one! You seemed to believe (as did the person I was responding to) that C# was a Windows only thing. That hasn't been the case for a very long time, and it is completely ridiculous now a days. In either case, it might seem we agree if you think that people are basing their views on obsolete information. But that then rather begs the question of why is that so especially the case here. If I was discussing e.g. javascript frameworks from the perspective of somebody 4 years out, let alone a decade, I'd be quite justifiably skewered. In other fields, 4 years ago things like TensorFlow did not even exist as public projects. 4 years is a very long time in software, so why are people so particularly slow on the uptake in this instance? Bias, bad marketing, something else?
[1] - https://web.archive.org/web/20060421052106/http://www.micros...