Even with bullying procedures in place, most workplaces are made up of complex and informal networks, empires and factions that can aggressively protect powerful managers accused of bullying. Often victims are bullied more after they make a complaint, often with an abuse of performance management so the victim is made to look incompetent or disgruntled, or the actions somehow justified.
It's not uncommon for co-workers to turn against people who make complaints to protect and even advance their own careers. In my experience, it is often the victim who leaves the workplace with a career in tatters, while the bully gets slapped on the wrist and is eventually promoted once again.
Mobbing is also used to describe a situation where co-workers, subordinates or superiors "gang up" on someone in an effort to force them to quit, to force them out of the workplace. This is done through behaviors that can be very blatant or quite subtle. They may do this through rumor, intimidation, humiliation, innuendo, isolation or discrediting. In short, they simply harass the person until they finally quit.
However, at the heart of it all, mobbing is malicious, general harassment that is neither racial nor sexual. It slips under the legal radar and walks some fuzzy ethical lines because it does not fall under the neat label that the law provides for workplace harassment. It is sneaky and underhanded and its perpetrators are cruel, narcissistic control freaks who thrive on their perceived feeling of power. They revel in the spoils that come from the abuse they inflict. As they see their victims cower and become more and more beaten down, they feel more and more powerful and in control.