The idea behind copyright is to encourage creators to invest their time and effort in creating works that will ultimately benefit the public by enabling those creators to profit from the work. The duration has changed with the marketplace because it needed to change with the marketplace. It may have changed too much but what you're proposing could arguably have a catastrophic impact in the arts.
Yes.....and the fact that copyright expiration doesn't allow new creative works. All it would do is allow a non-artist like me to make and sell exact replicas of something a talented guy like Jim had created.
The only benefits from copyright expiration are (a) the non-creative companies that make cheap replicas and (b) the public who wants to buy cheap replicas.