Why do the words, “I’m sorry” mean so much to Bri coming from Dr. Cook?

When Bri first sees Dr. Cook speak, she thinks he is racist and corrupt Bree is shocked that he refuses to acknowledge that Tate and Long abused their power and unfairly target black students. There is more to Dr. Cook and he changes his point of view. He says that he is sorry that the district let black students down. Bri is impressed with this. She thinks that change is possible in some people.