Fear: John Proctor fears the consequences of speaking out against Abigail. He knows that she is powerful and influential in Salem, and he worries that if he accuses her of lying, he will be putting himself and his family in danger.
Lack of evidence: John Proctor does not have any concrete evidence to support his claims that Abigail is a fraud. He has seen her behaving strangely, and he has heard rumors about her, but he does not have anything that he can present to the court as proof of her guilt.
Reluctance to betray Abigail: John Proctor has a complex relationship with Abigail. Although she has betrayed him, he still has some feelings for her. He is reluctant to expose her as a fraud because he does not want to hurt her.
Desire to protect the innocent: John Proctor knows that if Abigail is exposed as a fraud, many innocent people will be exonerated. However, he also knows that speaking out against her could lead to violence and upheaval in Salem. He is hesitant to take action because he does not want to be responsible for causing harm to others.
Ultimately, John Proctor's hesitation to expose Abigail as a fraud leads to the tragic events that unfold in the play. If he had spoken out sooner, he might have been able to prevent the deaths of innocent people. However, his fear, lack of evidence, reluctance to betray Abigail, and desire to protect the innocent all contributed to his silence, which allowed Abigail's lies to continue and the trials to proceed.