Why was Elia Kazan's testimony to the House Un-American Activities Committee (HUAC) self-serving?

Critically-acclaimed and commercially-successful director, Elia Kazan, was a member of the New York City chapter of the American Communist Party. He was also a member of the Group Theatre, a theater collective in New York City, and many of its core members were also part of the American Communist Party. During the investigative period of the House Committee on Un-American Activities in 1952, Kazan was called to testify against members of the American Community Party, particularly to reveal the identities of members.
Kazan would later refer to his cooperation as a "friendly witness." This is the first evidence that Kazan was not forced to give up the names of his friends and colleagues in the American Communist Party and Group Theatre. Kazan would also later state in his memoir that he was resentful over a dispute with his colleagues at the American Communist Party. He claimed that he was put to trial within the Party for an offense, and this made him embittered. This, Kazan claimed, was one of the motivations for his decision to betray friends and colleagues.
Although, as he expressed later on in life, Kazan thought of self-preservation (in terms of evading possible jail terms or oppression from the United States government) at the time of his testimony.
It could also be speculated that Kazan was trying to preserve his successful career. Although Kazan's testimony would alienate himself from numerous film industry colleagues and former-friends, the controversy did not greatly affect his career. Three years after his testimony, he released one of his most successful films, East of Eden, starring James Dean.