Short answer: In Pirates of the Caribbean, Barbossa and the cursed crew needed Bootstrap Bill’s blood (via his son Will Turner’s blood) to lift the Aztec curse because the curse requires payment in blood from each person who took a piece of the cursed treasure. Bootstrap’s blood was the original missing piece in the repayment chain, and Will Turner, as Bootstrap’s son, carried his blood in him, so they sought him out to complete the required blood debt and restore their humanity.
