I see an average of ~44 deaths total deaths per year with an average of ~2 murders per year attributed to left wing extremists while ~33 murders per year are attributed to right wing extremists.
The ADL website also says that left wing extremists are more involved in destroying property and that the higher number of people killed by right wing extremists are killed during spree shootings, few incidents - high body counts.
The operative word, regardless of political leaning is "extremist".
These people do not represent your everyday, run of the mill, garden variety individuals.
Left - 5,000 arsonist, looting, property destroying, riotous, extremists kill 1 person
Right - 1 extremist kills 25 people
Pray tell, how many separate incidents resulted in the 443 cumulative deaths in the 10 year period?