They're insecure and have many unresolved issues including anger. It's easier to look outward than inward.
There is a difference between judging others and judging behaviors. I believe we are to discern good behavior from bad behavior, meaning do no harm everyone. Don't lie, steal, cheat, murder, etc. Does it mean that we need decide a person is bad because of their behavior? Not necessarily. Should we talk to a friend if they are harming others? YES.....BUT, as a general rule, we are to look far more into our OWN behavior and if we are focused on our hearts, we will not have the time to finger point. Sometimes my husband says, I don't like your attitude toward that person. Is he being judgmental? No. He loves me and has a knowledge of my actual heart, so when I am out of alignment, it is right for me to hear correction. Sometimes people are so concerned with being judged, that they forget that maybe they need to be told when they are hurtful.....at the same time....I would NEVER tell someone they are headed for Hell....only God can truly judge the heart....and that is what not judging is about....not judging intentions. We are incapable of judging intentions....that is why is says, "But by the grace of God go I," as my walk is different than that of others, and if I have an easier time in an area, maybe it was the difference of my parents. I am to pray for others....not judge them. Sorry if this answer is long, but there is so much misconception on this subject.
Human conditioning. Wolves in sheep's clothing try to mimic and mock the Shepard.