You could argue that 14 years is a little short, especially for books which can get adaptations that pay more than the book. OTOH preventing adaptations stifles things. Imagine if Tolkein had managed to lock down his orcs and elves like Disney locked down the mouse.
I think 20 or 30 years is fairer. But IIRC it's not about fair, the Constitution says that it should only be to encourage innovation, and long copyright inhibits innovation.