Laman and Lemuel's hearts were not totally past feeling, but it required a spiritual sledgehammer to make them feel. Only in the face of absolute desperation were they able to make the connection between their troubles and the binding of Nephi. Even then they may not have seen that as causative, only that Nephi had demonstrated a connection with the Lord in the past, and they clearly saw the need for divine intervention. It is even likely that they did not see themselves as the cause of the problem. Those who have been able to learn to kick against the pricks are usually adept at the kind of self-justification that could easily have self-exculpated the brothers.