I can tell you the reason for this is because the right is far more organised than the left. This can be a bad thing but when you have the proud boys who are able to organize and promote to other members to not act in a vigorous or deadly manner when out on the streets it, in total, ends up in less attacks and organization on this level, in this context is good. While antifa are all individuals without a leader and only radical ideals and burnt out social policies (communism) to lead and inspire them you can see why a group formulated like this would end up causing more civil unrest and chaos in their wake.

https://www.newsweek.com/antifa-far-left-violence-extremism-deadly-year-opnion-1477065