Bullying persists because it is rewarded with social status and sex, so people that can be bullied are a very valuable resource. When an animal looks for a resource, it looks for the most easily available resource. This just happens to be people that are vulnerable and not likely to strike back, which both applies to people with autism.
NT accept bullying as normal behaviour as the vast majority of themselves have too participated in it. To denounce bullying is to paint themselves as wicked so only the innocent few will do this.