While the Windows Compatibility Pack was released in 2017, with 20,000 APIs added to .NET Core for Windows, Linux, and macOS, making it easy for developers to move code from Windows-oriented .NET Framework to cross-platform .NET Core.
As .NET Core enables web apps that can easily scale and run on Linux, the addition of the .Net Framework APIs made it even more resourceful.
How Microsoft .NET adoption gets bolstered by open source?
The .NET framework originally ran only on Windows, before Microsoft first considered sharing the .NET Core on GitHub. At the time, GitHub was a relatively unknown platform for many of its developers, who obviously had a lot of questions about how the platform worked.
Now, several .NET customers who historically composed their apps using Microsoft-supplied libraries, which were closed-source, are comfortable depending on non-Microsoft libraries, which are typically open source.
Therefore, open source is the most sustainable way to build a stack with wider support, over an ever changing development landscape of operating systems and architectures.
Why open source is important for the .NET project?
Admittedly, modern developer stack needs to be cross platform, as open source is the most sustainable way to build a stack and enables anyone to view, debug, and contribute to the runtime used to build their application.
Thus, open Source has helped ensure that the .NET project is fully available beyond a single vendor, that is, Microsoft.