A book is usually a single work attributable to a single author (or a group of authors). And you don't usually stream a book as "let's stream pages 175 to 185" [1]
In case of music assigning ISBNs to CDs doesn't really work because people more often than not listen to, stream and broadcast individual tracks. And there's no global ID system for individual tracks. This becomes even more messy when you consider that "Original performance 1983", "remastered 1994", "best of 2003" and "Japanese Christmas Special 2013" are all different tracks (even if it's the same track with the same song), often has different distributors and rights holders, and people will fight to the death defending a particular version :)
[1] Audiobooks are a slightly different beast, but they are still much easier to match to an author.
In case of music assigning ISBNs to CDs doesn't really work because people more often than not listen to, stream and broadcast individual tracks. And there's no global ID system for individual tracks. This becomes even more messy when you consider that "Original performance 1983", "remastered 1994", "best of 2003" and "Japanese Christmas Special 2013" are all different tracks (even if it's the same track with the same song), often has different distributors and rights holders, and people will fight to the death defending a particular version :)
[1] Audiobooks are a slightly different beast, but they are still much easier to match to an author.