What you asked is a nice question and it shows you're paying attention to the community to observe somethings..
I myself do not know the actual post which are specific to pob community unlike CTP, Stem, weed, natural medicine and sports ltalk etc that have barriers to know you can post or tag to post in there community.
I myself do call Pob the heart of Hive, in my own understanding I define it to be the ground or platform that accommodate all posts in the ecosystem as a result of creativity.
I say that because when you take time to check you will see most post from other community that tag proofofbrain to there posts while proofofbrain post are limited to an extent.
I will just say we post article that are relevant from all angles to the community.
Exactly-- The communities and/or tribes you noted have a specific focus. Proof of Brain is open to all topics.
At any given moment some topic or other is the topic, and that's what I'm trying to determine before I post. If my post is on a topic no one cares about, then no one will read it. No one wants to see 0 upvotes with 0 comments.