Maybe because in some countries (like Germany) it is not yet in public domain.
Which is what they do mostly. If Germany was the problem, they'd make the upload inaccessible in Germany and leave it untouched for everyone else. Content-ID marking it globally is clearly an issue on YouTube's end
No they don't. You must work under the fair use laws of every territory the content is available in.
The US has a significantly wider fair use law than almost any other country on Earth.
> If Germany was the problem, they'd make the upload inaccessible in Germany and leave it untouched for everyone else.
They do - it is extremely common for items to be blocked to Japan especially, as Japan has very tight fair use provisions in particular.
It will be "gemeinfrei", which is a different thing, somewhen after 2036. Probably even only after 2058, because one of the composers of the music lived till 1988.
EDIT: German Wikipedia says 2042.