If characters from films and television programs are able to become public domain, then this music, which everyone knows and recognizes, should also become public domain. You've seen many Star Wars themed jokes in television and movies, and if the writers are allowed to use that, then they should also be able to use Star Wars music.
Everyone knows and recognizes the Star Wars soundtrack. It is something that people who never even seen or heard of Star Wars know and are familiar with the sound. It is well known and used by virtually everyone. It is rare and uncommon for anyone to say that they do not know it.
The reasons the Star Trek Soundtrack should enter public domain are simple, they have been out in the public for over 20 years. They have become commonplace and recognizable to almost anyone on the planet.
As both a lover of music and of Star Wars, I believe the franchise earned enough money from the movies, action figures, food and soda, light sabers, helmets, comic books, magazines, books, and other memorabilia to make millionaires out of the companies that own the rights. It is time for them to give back to the public and music is the way to do it.
I don't believe that things enter into the public domain simply from being commonplace and well known. A period of time has to pass before the copyright runs out or it has to have been abandoned. Neither of those things apply to Star Wars as George Lucas is still making a large profit off of them and some new movies are in the works.
The very fact that the Star Wars anthology soundtrack is widely known, and liked for that matter, is reason enough to keep it out of the public domain. Everyone would zero in on it right away in attempts to make their fortune, this is unfair to the original creators and their rights and legacy. Star Wars is still so relevant that movies are continuing to be made, the public domain is for things old and not profitable to the original creators anymore.
No, the Star Wars anthology soundtrack has not become so commonplace and well-known enough that it should enter public domain, because something does not lose its copyright protection by becoming very, very successful. That is the opposite of the purpose of copyright laws. Something that is successful needs all the more protection.