Then they should get copyright for 14 years since publication, like in the first copyright law, the Statute of Anne. There is no benefit for society to extent copyright past that point, since it does not induce creative corporations to publish more works: profits 20, 50 years into the future are not relevant to current business decisions.

The original idea was that copyright is a compromise that maximizes the social welfare, people give-up their natural right to copy and share for a limited time so that more culture is created. Of course, once the system was set in motion, the holders of valuable works had a very strong motive to exert political pressure to extend the copyright to absurd lengths and push the notion of "intelectual property" at face value, instead of the original social compromise. No one was left to fight for the public domain and now we have these huge dynastic corporations that are strongly anticompetitive, using warchests of past works that new creators haven't yet amassed. If not for the internet and long tail consumption it enabled by lowering entry barriers, a few companies would own all comercial culture.