Or HaChaim on Genesis 41:27/אור החיים על בראשית מ״א:כ״ז

1 יהיו שבע שני הרעב, "there will be seven years of famine." The reason that Joseph did not describe the seven years of plenty as such in verse twenty six was simply that even during the present period food was plentiful in Egypt. The great plenty that would characterise the next seven years was not such a contrast to the existing conditions. The only thing that was different was that the adjective גדול could be applied to those years of שבע (verse 29). Joseph stressed only what would be radically different from the present.

2Inasmuch as the increased harvests during the coming seven years were merely designed to offset the lack of harvests during the seven years following, Joseph did not describe those years at once. The major message of the dream was the eventual famine.