Unity3d (a widely used game engine) ships with Mono, which makes modding easy for the developers to implement and the modders to use. Many hobbyist and professional programmers like to use Linux even for gaming, thanks to Steam’s Proton. But until now you can only mod on Windows. With the gifted code maybe it will be possible on Linux, too.
The gamers on Windows are happy because they get more mods, and it is also good publicity for Microsoft.