Answer:
Because he felt guilty and believed he deserved punishment.
Step-by-step explanation:
John Proctor is one of the characters in "The Salem Witches". He was a full and honorable man, married and had children with Elizabeth. Together the couple hired Abigail to help Elizabeth with household chores, however, John and Abigail had a love affair when Elizabeth found out she fired Abigail from her job. Abigail, angry, denounced Elisabeth of practicing witchcraft and later denounced John of witchcraft as well.
John knew Abigail is lying, but only tried to defend his wife, he accepted the accusations against himself because he had committed a sin, been unfaithful to his wife and put them in that situation, so he believed he needed to pay for his mistakes.