This looks like a perfect example of shopping-like question, because it directly asks about book suggestion. I thought that all shopping-suggestion questions are strictly banned across nearly entire SE network. What am I missing?
I don't think we've discussed this much. What we have in the help center just says that "resource location" is off topic:
Where to buy a specific part, "Which headset is the best?", etc.
The intention is to discourage people from asking which headset to buy, which flight planning software to use, or where to find spare parts for their aircraft. Those questions are very subjective and answers change quickly over time, so I think there are good reasons for making them off topic and most SE sites take that general approach.
But some resource questions could be useful and answerable, if they're asking for industry-standard reference materials or standard reference works on technical topics. The question you mentioned seems to me like it's in that category, and it's got enough upvotes to suggest that people find it useful.
As always, our standards are guidelines, not strict policies, and in the end every question is judged individually.
Book recommendations are not strictly banned across the entire SE network. Without digging far, I'll name three sites which allow book recommendations (within their community-specific standards): Mathematics, Cross Validated, Physics. And apparently, certain book recommendation questions are okay here, too.