Because if it's in the public domain, then what they're doing is not infringement, so those rules don't apply.
And giving them a taste of their own medicine only justifies the law and the outrageous fines. It won't make them want to change it. That's how they want the law even if it bites them from time to time.
Actually it's what happens when one video service dominates the field. There should be a mass exodus away from Youtube because of their policies, but there are few places people can go and get their fanbase to follow them.