compiling it for .NET on Linux

It always sounds so simple for the layperson. Just looking through the list of DLLs in the portable ZIP, PDN uses Windows Forms (System.Windows.Forms namespace), which, as far as I understand, isn't included in the cross-platform releases of .NET. They'd have to rebuild the entire UI with .NET MAUI or some other cross-platform toolkit. Then there are lots of other bundled libraries that may or may not work in a .NET-on-Linux environment.

Releasing and then supporting a second platform is never as easy as just compiling the executable. Figuring out the quirks and differences of various systems, especially one as heterogenous as the Linux ecosystem, is a drain on resources that small development studios often can't afford. Raiguard (hallowed be his name), one of the developers of Factorio, and the person who is single-handedly maintaining the Linux-native build, wrote a blog post about its challenges.