Why is the policy on book recommendations not clearly stated in the FAQ?
Because it has nothing to do with books... It's about shopping:
What’s the point of a bunch of labor intensive questions that provide only temporary benefit to a limited (some might say Too Localized) audience?
Read that blog post - it's focused on a particularly troublesome sort of shopping question that plagued Super User, but many of the same concepts apply - in particular, how you can get what you want:
when it comes to shopping questions, don’t ask us what you should buy — ask us what you need to learn to tell what you should buy.
As for why this isn't mentioned in the FAQ... It is. It's part of a much, much larger set of "poll" questions, addressed in the section titled "What kind of questions should I not ask here?":
To prevent your question from being flagged and possibly removed, avoid asking subjective questions where …
- every answer is equally valid: “What’s your favorite __?”
Very, very few people ever read every book on a topic. There are a lot of books out there. So if all you ask for is the name of a book, unless your topic is exceedingly narrow you'll likely just get suggestions and votes for whatever books are most often read. You could pull a list off Amazon and sort by popularity, and it'd be just as useful (not very).
What you really want are experts who could teach you all you need to know without a book to step in, give you an overview, and then point to a book that'll take you the rest of the way. So instead of having to come up with everything you want (from a position of ignorance no less!) before asking, you're able to ask first "what do I need to know" and then "and how can I learn it?"