That's actually a really good idea. Of course it is probably (unfortunately) politically impossible.
And, it can be morally justified -- if someone is sitting on the rights for a work, and isn't using it, then it makes sense to levy a tax against it as they are utilizing the expensive resources of the world governments in order to defend the copyright.
Who will swiftly pass the additional cost on to their customers. Voters who see it that way won't vote voluntarily to pay more just so content creators can keep their copyright.
There is no large concentration of wealth on the other side of the issue to support it, therefore it will never happen.
Sorry folks but that's how politics in the USA works.