> Almost no one thinks their code is copyrightable

I think this is an unusual opinion.

Code may not be copyrightable in as small chunks as you put there, but in terms of larger pieces I think companies and individuals very often labour under the belief that code is intellectual property under copyright law.

If code isn't copyrightable, from where comes the GPL?

And why does anyone care if (for instance) some Microsoft code might have accidentally ended up in ReactOS, causing that project to need to go into a locked-down review mode for months or years? For that matter why do employers assert that they own the copyright in contracts?

I think it's the opposite - almost everyone thinks their code is copyrightable, outside of APIs and interop stuff, or things so simple as to be trivial.