eclipse, that is because people don’t have the tendency to see themselves in the “wrong” and always believe they are “right”. Many people’s need to be right even supersedes their need to be happy. Those are the people that will argue with you to the nth degree and will never ever see another person’s perspective or point of view. They do not normally accept responsibility for their actions nor are they accountable for their actions. Therefore when they speak, make nasty comments, spread loshon horah, they don’t even realize they are doing it because they don’t put themselves in that category nor do they consider what they are doing as “wrong” or speaking loshan horah. They will excuse it 360 degrees until your head is spinning from the excuses and will never back down and just apologize for the comments.
Others who choose to improve themselves when confronted will be shocked at their lapse, apologize and take note to be careful in the future.