Linux printing is very complex. Before Foomatic came along you got to experience it in all it's glory and setting up a working printing chain was a pain. The Foomatic Wikipedia page has a diagram that will make your head spin.
No doubt, the kernel itself is also quite complex... but my comment here is on the user experience perspective, namely, for me at least "it just works". So I'm not trying to imply it will work for anybody flawlessly nor that it's due to the simplicity of the stack, solely that it works, for me.