Yosef initially said that the good cows and ears were seven [Stam] years, and did not mention the satiation. Why did he immediately explain that the bad cows and ears are seven years of famine?
Ramban, Ohr ha'Chayim: Because the good years were nothing exceptional. 1 And the novelty of the dream lay in the bad years. That was the main objective of the dream, to prompt Pharaoh to act, to save his people from starvation. 2
Moshav Zekenim: He wanted to alarm them, so they will worry how they will survive [so when they hear about the good years, they will be eager and zealous to save food - PF].
Kol Eliyahu: The satiation did not affect Pharaoh. Refer to 41:25:3:3. Ha'amek Davar - Had Pharaoh heard this, he would not have wanted to hear more. Therefore he first mentioned the famine; then, it is understood that the good years are in order to sustain the world during the bad years.
Ramban: As the Torah described Egypt as "the garden of Hashem" (Bereishis 13:10). Ohr ha'Chayim - Even though there will be great satiation, this is not as wondrous as the famine.
Why were the thin cows called Ra'os (evil)?
Ha'amek Davar: It is because they ate the good cows.
Why did Yosef call the bad sheaves "Rekos"? Pharaoh called them "Tzenumos"?
Ha'amek Davar: Pharaoh thought that although they were parched, there was yet a drop of grain in them; for he did not feel them. Yosef told him that they were totally empty.