They may be doing so because they think simple upvoting is a better way to to second recommendations. However, this isn’t really the case because many recommendations mention multiple books, so doing so would not clearly endorse a specific book.
Plus, upvoting doesn’t distinguish between “I agree that some or all of these books are good recommendations,” and “Thanks for suggesting some plausible sounding candidates.”
They may be doing so because they think simple upvoting is a better way to to second recommendations. However, this isn’t really the case because many recommendations mention multiple books, so doing so would not clearly endorse a specific book.
Plus, upvoting doesn’t distinguish between “I agree that some or all of these books are good recommendations,” and “Thanks for suggesting some plausible sounding candidates.”