I see why the author did this, building a video game with all of its resources (source code, shaders, assets, docs etc.) is actually very complicated.

But then I might ask why all of it needs to be build all of the time? Why not make dedicated build steps for every sort of resource and maintain a global build script for all? Doing it the KISS way seems more practical to me than inventing a completely new tool. This is my approach to build software for 20 years now, and it never failed me.