Because the makers aren’t selling you the software or the video. They are selling you the rights to consume it. The reason for that is that software, movies and books can be easily copied and redistributed.

When that stuff was on a physical medium it was also sold with the same license. You would own the disc/tape/book with the license but you wouldn’t own the movie, software or literary work. You can sell the disc with the license but you can’t take the content of the disc and sell it separately since that is technically copying and you don’t own the copyright.