The fact that the authors death factors in at all automatically makes a young person's IP more valuable than an old person's. That's a really dumb system. It should expire x years after creation and the author's death should be irrelevant.
It preserves the “you own your work for your natural life”. Whether that’s what copyright should be is a separate question, and I think the answer is absolutely not, but easier to change gradually than all at once.
I agree X years after creation sounds like a much better system though.