I agree that many books were bad simply because the authors could not write well and had no idea about pedagogy. I think the number of people who knew something about a particular subject was just smaller and that's why it wasn't questioned much by the publishers.

Another reason may be the fact that a lot of information could not yet be found on the Internet. That is why some authors were more interested in listing the information than in pedagogical communication. The result were books like "Chapter 1: How to start the compiler from command line", "Chapter 2: List of all functions of the standard library", no chapter 3.