Why does the Torah see fit to inform us that that entire generation died out?
Seforno: Because that was when Bnei Yisrael reached the lowest levels.
It seems from this verse, that the subjugation to Egypt began only after Yosef and his brothers died. Why was this so?
Maharal (Gevuros Hashem Ch. 9, p. 54): Refer to 1:5:1.02:1; only now that the Bnei Yisrael numbered 70 was it possible that they would be subjugated to Mitzrayim. However, Yaakov and his sons were not themselves worthy of being enslaved; 1 except that they were a part of the inclusive number of 70. 2
Maharal: We find that when Yaakov passed away, he was no longer included in that number, and he was immediately returned to the Holy Land. (The Shevatim's bones were also returned - but only later, upon the Redemption.)
However, Rashi to Bereishis 47:28 implies that the Mitzrim began to subjugate Bnei Yisrael immediately upon Yaakov's passing; refer to Bereishis 47:28:2.3:1, and to Bereishis 50:15:1.1:3.
Why does the Torah need to inform us that "Yosef and all his brothers died"?
Hadar Zekenim: To teach us that Yosef died before his brothers - because he conducted himself with authority, and kingship buries those who possess it! 1
Which also explains why the Nevi'im far outlived the kings. Also refer to Bereishis 50:25:151:5.
