Since - as only one example of the complexity involved - the music used in the film is almost certainly licensed and must be paid for, and the studio does not "own" it, there's no way that they can simply release it for free distribution or put it into the public domain...
And having had this issue myself with a Hollywood movie, where the rights for the music in the final cut were too expensive, trying to replace the music is always horrible. Especially, as in this case, where you would likely have to go with public domain music.
