In the following position, McDonald states that `14. d4!` is the move that gives a large advantage to White. 

```
r1bqr1k1/2p2pp1/pbn4p/1p1np3/P7/1BPP1N2/1P3PPP/R1BQRNK1 w - - 0 14

```

However, `14. axb5` wins not one but two pawns and without any unnecessary complications, such as opening the center up and allowing Black some freedom.

After using Stockfish to verify this, I wonder why (or how) GMs write mistakes in opening books, when they have engines to double-check. Why does this happen?