The copyright doesn't relate to the concrete or actual strip of film, it relates to the concept. It protects an abstract piece of property. When you buy a DVD, you don't own the concept, you only own the piece of plastic.
I'm not saying the copyright attaches to the plastic disc. That is why blank DVDs are not copyrighted.
But the content is, whether it's a DVD, CD, book, canvas, the internet, whatever.
Nobody can advocate altering the contents of a book, for example, and selling that for a profit, but they see no problem with editing a movie for distribution. Strange.