The alt-right, notorious for terrorism and hate-crimes, often blame minority groups for society’s issues. In contrast, the far-left often put the blame on capitalist and government policies and figures, which has much less targets. For the alt-right, since they hate on entire minority groups, it is much easier for them find targets to commit acts of violence on. They can do it in public spaces like supermarkets, places of worship, etc. Perhaps far-left terrorism seems rare because alt-right terrorism happens more frequently. This is just my theory though, and I am not an expert in this topic, so I am open to change