A Layman's Questions

Why is looking back such an egregious criime to Christ

Luke 9:61-62
61 Still another said, “I will follow you, Lord; but first let me go back and say goodbye to my family.”
Jesus replied, “No one who puts a hand to the plow and looks back is fit for service in the kingdom of God.”

There are many such verses as the one above we are also plainly warned that you can't love the world and God and in the Old Testament the most famous example is Lot's wife turning to salt, Yet what is looking back while King Saul fell from the position of authority because he looked to man he could not be said to look back, Samson though constantly unfaithful was not accused of looking back. In the New Testament, in Acts 8, Simon the Sorcrer wanted the power of God for selfish gain but this appears to bot be looking back. With many sins great and small looking back seems especially egregious Like a married individual wanting a former lover.