Because abusers (both physical and emotional) are deeply insecured. They don’t have the courage to face themselves. They have gas lighted themselves into believing that they are a good person. They try so hard to prove this picture of themselves infront of society. This is why most abusers come across charming and people loving person infront of general society.
They feel better about themselves by stepping on their victim’s happiness. They feel even more better when they play victim card and receive sympathies from others. They don’t have enough maturity to accept and address their own insecurities. Therefore, the way they deal with their insecurities are by pulling victim down. Believe it or not, they get sadistic pleasures from it.
No abuser want to accept the fact that they are being an abuser. Therefore, they give endless justifications and reasons for the BS they do. On the other hand, emotionally healthy and matured person will be willing to address & work on problems and oriented towards wellbeing of themselves and others. This is the difference between normal humans and abusers.