People may feel "consequences free" for a bunch of reasons.
At least, anonymous internet users don't know so much about you and your past to compose really humiliating statements. They can make only random or semi-random insultings, basing of what they know about you online, and online you can (at least partially) control information about each of your internet avatars.
But people, who know you for long IRL, can resourcefully use your most painful complexes and events, caused you strong guilt, shame or pain, to humilitate you as hard as they can. Also they can express their disgust to you through voice and gestures, yell at you, spit at you, beat you in variety of ways, take off and throw away your clothes, dunk your face in a puddle - whatever their imagination allows.
Such a things often happens in low-life, low-educated collectives (especially when these collectives consist of kids and teens), problematic families, also in army and in jail. So... I tell you, real life opens much more rich opportunities to abuse people, than internet.