In Chapter 19 of To Kill a Mockingbird, why doesn't Tom want to explain why he helped Mayella when he is giving his testimony?
Tom is reluctant to discuss helping Mayella because he does not want to seem like he pities Mayella. Remember, he is facing a racist jury and system. He needs to tread as lightly as possible. No doubt Atticus has made him aware of this too.
In fact, it is under cross examination that Tom makes his biggest mistake: he acknowledges that he helped Mayella out because he felt sorry for her. Mr. Gilmer jumps on this immediately, making sure the jury is aware that a black man, who in Maycomb is inferior to even the lowest of white people, feels sorry for a white woman. Stating that is Tom's biggest mistake while testifying, and one that seems to have the biggest impact on the jury.