A hundred years ago, when economy and business were still at rational levels, things like patents and copyright made sense.
A patent was a government-supported way of an inventor of a physical device to get reasonable economic profit from his invention without any competitor stealing his invention. This protection was given for a reasonable amount of time, something like 10 to 20 years. After that it was seen fit that the invention becomes "public domain" in that anyone can improve on it.
Copyright was the same thing but on artistical creations, such as books or music. For example in the United States the Copyright Act of 1790 gave rights for just 28 years in total.
This was later lengthened to rather ridiculous proportions, though. For example the US Copyright act of 1976 set the copyright length to the life of the author plus 50 years. If the author lived eg. 50 years after writing the book, the copyright on the book would hold for a whopping 100 years. Moreover, the newer Copyright Term Extension Act of 1998 lengthened this even more by adding 20 more years.
Patents still have a rather reasonable expiration date (for example the infamous LZW patent (used by the GIF format) has expired in all countries where it was applied, which is a rather big relief, really). Copyright has gone completely crazy. The only reason for this extension of copyright has been the lobbying of huge megacorporations.
One of the most prominent megacorporations which lobbied the US government to pass the copyright extension was Disney. Disney is rather infamous for viciously defending their property and their copyrights. Their oldest creations, including their Mickey Mouse character, were in danger of passing to public domain, and this was rather unthinkable for them. Luckily for them they were able to lobby the government to extend the copyright. For this reason the 1998 Act is sometimes pejoratively called "the Mickey Mouse Protection Act".
Quite curiously, Disney, a big promoter of copyright extension, is quite hypocritical in this regard. They themselves have used pieces of art which have become public domain by natural expiration to create new pieces of art of their own. For example their "The Jungle Book" movie was created only seven years after the copyright of the original book expired. Disney has got millions of profit from this movie and its merchandize.
As with patents, copyright has changed from a law which protects the individual to a law which boosts megacorporations, from a law that protects individuals from unscrupulous corporations to a law which gives unscrupulous corporations weapons against individuals. The difference is that copyright lasts way too long.
Why does copyright last so long? What is the reason? Why is this reason different from the reason why patents expire in a rational amount of time?
Megacorporations have lobbied governments to extend copyright simply because of a few key popular concepts these corporations have (such as Disney's "Mickey Mouse"). In the process, however, everything has now a practically infinite copyright. In practice this means that enormous amounts of art is laying completely unused, protected from anyone who could have a better use for it, protected from people who could actually enjoy it. Corporations don't get any profit from these, but they viciously defend their rights to them. One wonders why.