Jamieson, Fausset and Brown on Genesis 40:23

23. yet did not the chief butler remember Joseph--This was human nature. How prone are men to forget and neglect in prosperity, those who have been their companions in adversity (Am 6:6)! But although reflecting no credit on the butler, it was wisely ordered in the providence of God that he should forget him. The divine purposes required that Joseph should obtain his deliverance in another way, and by other means.