The explicit, stated purpose of copyright was to encourage sharing of ideas. When it lasted originally 14 years, it worked. Before that, you might have had a great idea and kept it to yourself because why take years of your life researching a subject and writing a book when a publisher's going to immediately copy it and pay you nothing? 14 years is plenty of time to get a return on your investment and most importantly, after that, it didn't belong to you anymore. It belonged to everyone.

For example, that would mean District 9 and Hunger Games would be in the public domain right now.