Part of this stems from a pre-internet mentality. "Of course I need a full function reference! Where else would I find it?" Now you just Google it. A thinner book can leave the reference to the search engines, but for some reason this older way has become entrenched.
Yes, but that attitude is not dead: how many projects have you come across where the only documentation is the JavaDoc or equivalent? It allows someone to tick the box that yes the documentation is done, with minimal effort, but it's not that useful to the next programmer, who really needs sample code, oh, I get this from that, and this from there, then I feed them both to the function...
You had man pages, which are as good if not better than what you might find on Google. If you were writing C programs on a UNIX system, everything you needed was there. No need for K&R to kill trees putting all that in their book.
