Here's why:
* Racist Attitudes: Aunt Alexandra represents the deeply ingrained racism of the Maycomb society. She believes that Tom Robinson is guilty simply because he's Black and the Ewells are white.
* Social Standing: She is concerned about maintaining the Maycomb's social hierarchy and the family's reputation, even if it means upholding a blatant injustice.
* Pressure on Atticus: She tries to pressure Atticus into dropping the case, believing it is bringing shame upon their family and causing them social isolation.
Although she never explicitly says Tom is guilty, her actions and opinions throughout the trial reveal her deeply ingrained biases. This conflict between her and Atticus highlights the central theme of racism and prejudice in the novel.