I see all kinds of "small organizations" forming in Slack communities, subreddits, and other online spaces. Some might be described as influencer driven communities like substack. Or audiences of a specific podcast. And so on. It's almost never been easier to participate in one of these "organizations".
Even locally, where I live, the school board, city council, local advocacy groups, etc are heavily attended. We have a local group advocating for immigrant rights. Another YIMBY group. Another group that argues against the YIMBYs. PTA meetings. Another group that advocates for the homeless.
I'd say its true that many are in the "universe" of one political sphere (in my case left-leaning). But that does not mean they have been wholly subsumed by "The Left", they often disagree and fight against "Left" politicians. And often "The Left" is not a uniform thing in a city with differing interests and stakeholders.