Because they are meaningless. Because they aren’t real. Because their intent was only to manipulate.
https://www.psychologytoday.com/blog/understanding-narcissism/201708/why-do-narcissists-abuse-those-they-love?amp resonates a great deal. In short, they enjoy the torture.
“When people have a Narcissistic Personality Disorder, two things interact to predispose them to be abusive:
1. They are low on emotional empathy.
Emotional empathy is the capacity to feel what another person is feeling (or what you imagine the person is feeling). Having emotional empathy decreases the likelihood that you will want to hurt others, because you will literally feel some of their pain. Without emotional empathy, you have less motivation to pay attention to the pain that your words and actions cause a partner.
Narcissists can have “intellectual empathy” without emotional empathy. Intellectual empathy is the ability to cognitively understand that you are causing another person pain. It requires that you stop and think about what the other person might feel in response to your actions. Narcissists, therefore, can understand that they may be causing someone pain, but they have less motivation to care because they are not feeling anything negative themselves.
2. They lack “whole object relations” and “object constancy.”
One of the main reasons that people abuse others whom they profess to love is that they lack whole object relations and object constancy. Briefly defined: “Whole object relations is the capacity to see oneself and other people in an integrated and realistic way as having a mix of good and bad qualities, some that you like and others that you dislike.” If you have whole object relations, you can accept that someone is not perfect and still value that person for the positive qualities he or she has. “Object constancy” is the ability to maintain your positive emotional connection to someone whom you care about while you are feeling angry, frustrated, disappointed, or hurt by that person. Object constancy helps you rein in your impulses to hurt someone during a fight. Lacking it makes people more willing to emotionally and physically damage their mate.”