HN has always had this pluralistic bent, because that's the way the site founder is. The word for pg's taste is 'catholic' in the original sense. So the appearance of a book on child-rearing isn't a decline or even a change; the question is whether the book is interesting, not what it's about.
It would be concerning if unpredictable, unrelated things didn't appear, still more concerning if all the things made sense and were correlated with some (any) convention, and most concerning of all if the convention were that of a majority.
It would be concerning if unpredictable, unrelated things didn't appear, still more concerning if all the things made sense and were correlated with some (any) convention, and most concerning of all if the convention were that of a majority.