Because the book tries to produce a narrative where new features are introduced out of obvious necessity: in this case, encrypting more than a block. And you ca

Because the book tries to produce a narrative where new features are introduced out of obvious necessity: in this case, encrypting more than a block. And you can do that with modes of operations or "native" stream ciphers. Essentially I'm handwaving and pretending that e.g. AESCTR is just a stream cipher :-)