That, and also that categories like offensive can be so subtle and context driven (eg "Get out of here" could be a jokey play between friends, serious advice in

That, and also that categories like offensive can be so subtle and context driven (eg "Get out of here" could be a jokey play between friends, serious advice in a generous situation or a rude retort). And then there's the sheer volume of training material which makes dealing with it a huge challenge, which is why researchers are exploring ways to shortcut the processes as they do here using additional LMs to help with their main LM.