You're being really pedantic when you say there was already Microsoft support for .Net on non-windows platform.

It was a unsupported (no release after 2006) bare fork of the runtime that couldn't be used commercially [2]. Would you have corrected me if I stated "Internet Explorer doesn't run on Mac Os X" just because there is a version of it from 2003?

Especially when you compare it to a large part of the toolchain including compiler and runtime under a MIT license that builds to multiple platforms from the same codebase [1], that's not even in the same league.

[1]: https://github.com/dotnet/

[2]: From your own "This license [...] allows for personal or academic usages, but they can't be used for commercial products"

While you're technically correct, ROTOR hadn't received any updates for a long time, and the source was licensed in such a was as to make sure anyone who could benefit from it running on *NIX platforms was heavily incentivized not to do so.

.NET Core works on Rotor for Linux and macOS, right. Silverlight for macOS also works on Rotor AFAIK.