Why separate documentation from code?

One thing that I find a bit strange in software development is that the documentation associated with development (design, requirements, notes, roadmaps, todo lists, bug reports etc) are all usually separated from code, particularly for “enterprise software”.

Why do this though? The only thing that truly defines the application is the code. So why not keep it all together and maintained in the same version control system? You still may not ever look at the documentation again, but at least you know where it is then 🙂