There are two phases in the life span of a creative work, namely when the author has an interest in the work, and when he has lost interest in the work. There is more to it than that: there are different types of interest, interest may be rekindled, and one interest may be worth more to an author than the other. However, I do not think it is a stretch to state that interest is high near the creation of a work, and gets less as time progresses: the author, eventually, loses interest, and then he dies.
Copyright law is there for several reasons. Actually, if you are American, you believe it is only there for one reason: to protect the interest of the public. The author’s interests do not enter into it. At least, that’s the theory, modern US copyright law very much aims to protect the interests of authors, and especially those of publishers. (Don’t ask me how they got to be in the picture.)
In Europe, we believe that copyright, apart from incentivizing authors, is mainly there to reward authors, and because they gain a natural right by creating a work.
The interesting thing about copyright law, is that it more or less presumes the interests of the author to be unchangeable. Not only that, but it tries to protect these interests as if they are at their strongest.
Of course, the public loses out big time in this scenario. When an author has lost all interest in a work, the public is still not allowed to mix, rip and burn it.