People do on occasion, like there were armed leftists that prevented police from raiding encampments in Texas, and at some protests there have been organized armed groups like John Brown Gun Clubs or Socialist Rifle Associations. Several people that argued for more militant resistance to state violence were murdered in 2020, and many times for decades before that, so a lot of people are scared and not organized sufficiently, but there are groups that have been preparing.
Republicans only rank so high for gun ownership because of the dozens of people that have an armories worth. Left -wing and marginalized people will have one or two guns that are effective, not a stockpile of tacticool attachments and WW2 rifles.