But it takes a good bit of time for something to become "traditional"; long enough that it becomes hard to figure out who, exactly, owns the copyright to what,

But it takes a good bit of time for something to become "traditional"; long enough that it becomes hard to figure out who, exactly, owns the copyright to what, as in this case. Limiting the term of copyright also has a function of promoting legal certainty: with relatively short terms, if there's a controversy, the court can have living witnesses and a fairly complete record, vs. a few strands of unconclusive evidence like here.