Mickey Mouse and John Coltrane are widely and continuously available because people enjoy them. If their copyrights expired tomorrow there would still be plenty of Coltrane MP3s and torrents out there a year from now. However try playing Coltrane in your restaurant without paying a license or try uploading Steamboat Willy to youtube to show the world this strange old cartoon you found. Then you'll discover that people are prevented from enjoying these works because companies are using copyright to remove them.