We understand that Peterson didn't write the book. Literally no one is saying that he did.
The book itself is a compilation of interviews, blog posts, speeches, etc that he and his daughter have done regarding their carnivore diet. Everything in it is something one or both have them have gone on record saying.
Also, Peterson isn't being "scammed" out of his content. The Amazon page states that $1 of every book sold goes to Peterson and his daughter