Why did the Montgomery bus boycott last so long?

The reason the Montgomery bus boycott lasted more than a year, from December 5, 1955 until December 20, 1956, is that the city refused to integrate buses until the US Supreme Court declared its policy was unconstitutional in the case of Browder v. Gayle,(1956). Although the Court's decision was released on November 13, 1956, the city didn't desegregate until it was served with a court order on December 20.