A question can be asked, Didn't Isaac and Rebecca still remain in the city? These were without question righteous people?

I would like to propose the following original answer, Bezrat Hashem, as follows: A person has to realize that each and every "TZADIK" is unique in his service to G-d. Therefore, when a "TZADIK" (Righteous man) leaves a certain location the impact of his leaving is still felt eventhough other righteous people might still be present in that same location. We must appreciate that each and every person has a soul that is unique to himself. Jacob's uniqueness was surely missed when he left Beer-sheba. Jacob was inherently different than Isaac and Rebecca because his soul was inherently unique. Therefore, the city changed when Jacob left Beer-sheba.

We can all learn a very valuable lesson from CHAZAL in this matter. Its good to try to copy and emulate the righteous, yet we must all try to developed the unique greatness that is inherently found in our own personal soul. That's why G-d made us all different.....