That's true. And there's the additional factor that the more familiar a topic is, the more likely the thread is to fill up with generic comments about it. That's what the HN guidelines call generic tangents:
https://news.ycombinator.com/newsguidelines.html. Those are probably the most repetitive kinds of thread, and therefore the least valuable.
This phenomenon shows up in most political threads but also in threads that aren't particularly political. The more generic topics have so much mass that they act like black holes that suck in all the interesting discussion (https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...).