Because Jacob and Joseph were both faithful to God; Joseph was able to forgive his brothers’ treachery from so many years before.
It was God’s will for the chief butler would be freed only to forget about Joseph’s request (Genesis 40:14). There have been a few times when we’ve wondered why we can’t seem to move up and do better. It may not be because of what we’ve done. Remember this passage where Joseph was forgotten for a divine reason. It could be because of what we’re about to do and that brings glory to God and be a blessing to others.