So? Of all the aggressive things the US forces upon the world (or just unilaterally does, ignoring agreements), undoing its own bad policy would be a drop in the bucket, and would be doing some good for once. I'm sure if we just did it, others would respond tit-for-tat and require registration of our material, and then mission accomplished.
(And at the end of the day, sovereign people are never required to do anything. The concept of international law is an oxymoron)
I don't believe it is a bad policy that copyright on anything that is copyrightable is automatic (I don't need to register this comment with the Library of Congress).
... And it would require renegotiating the treaty with all of these countries so that AI training is easier. https://www.wipo.int/wipolex/en/treaties/parties/231
... Or it would require the US to withdraw from the WTO and pass new laws for how copyright works.
I don't believe that neither the renegotiation nor the withdrawal would be something that would be done.
... And I believe that automatic copyright (as has been part of the Berne Convention since 1886) is a good thing.