After Yosef reveals his identity to his brothers, they are nervous and then overjoyed. They tell Yosef that they will bring Yaakov back to Egypt, to see him. Once all of Yaakov's children and grandchildren arrive, they are given the land of Goshen. The Posukim have a sense of finality in them, describing how the Jews settled in Goshen and gained Paroh's favor. Why did they all come down to Egypt? Couldn't they have just visited for a few months, then returned to Canaan? Why settle permanently in Goshen?
The reason that there was a horrible famine affecting the entire Middle East, and only Egypt had food. Anyone would jump at the chance to live there. Once Yaakov arrived, Hashem blessed the land and the famine ended. If he wanted, Yaakov could have returned to Eretz Yisrael, with or without Yosef. Yosef could just quit his job, since the famine was over he was no longer needed. Even if Yosef stayed, Yaakov still could have returned with at least one of Rachel's sons.
In retrospect, it was obviously Hashem's will that B'nai Yisrael be enslaved, but if Yaakov knew what would happen he would have left immediately. The logic Yaakov used, by which he concluded to settle in Goshen, is a logic which his descendants have used throughout history. Once Jews settle in a place where they are comfortable, they are reluctant to leave. When Yosef was alive, B'nai Yisrael were treated royally. Likewise, until the Spanish Inquisition, Jews held high, powerful positions in the Spanish government. German Jews were also highly respected, as bankers and merchants. So, even though in Yaakov's heart he knew he shouldn't stay, he and the rest of B'nai Yisrael got too comfortable in their foreign home, and could not force themselves to leave.