That's the problem. Stockfish has no opening book. While there is no doubt Stockfish can play stronger with good opening book, keeping a book up to date with e

That's the problem. Stockfish has no opening book. While there is no doubt Stockfish can play stronger with good opening book, keeping a book up to date with engine changes is really a full time job. So Stockfish project does not have any official opening book. Personally, I think using publicly available Komodo book would have been enough, but obviously Komodo book is tuned for Komodo and everybody would complain about any book problem. In a sense, "no opening book" is the official upstream supported configuration, so it is entirely a defensible choice.