The purpose is to incentivize creative works for the public benefit with the limited time exclusive rights, not retroactively extend copyright years after the death of the author to enrich their rights-holders in perpetuity every time expiration comes up.
As it is, you can't even make something public domain yourself - the best you can do is add a permissive license since all rights are reserved by default without registration.
But this is getting somewhat off topic.
The specific wording of the US constitution was (is?) a nice little bit of fluff but it didn't really change the nature of copyright at all when it was published.
There was a governmental agency (Hadopi) that costed millions of euros and due to the stupid law managed to won I think one case for 2000€.
They got merged into another useless agency and was forgotten. I am not sure whether they still exist, nobody really cares.
This is how pay of our tax money is spent in France, on subsidized sandboxes for politicians.
At the same time they got caught red handed disregarding copyright themselves multiple times (Sony's rootkit which used some linux copyright IIRC, or the case of several major record labels releasing compilation albums of music without artist consent and copyright in Canada are just two examples). By their own calculations used against file shares the damages should have amounted to billions, but they got away with not so much but a slap on the wrist. I wish some judge would have really made an example of some of them.