Because it was made to run on Linux from the start. I remember being excited to work with .net core on Linux, then discovering that most of the system libraries for network programming and related were either not implemented or badly working, but you would only find out if dug deep into low level stuff. After that, I swore of using it seeing how much the hype for cross platform didn't match reality. Hopefully they fixed it, but seeing as there are other choices of languages, it wasn't so bad.
