It's for discussing on-topic topics of interest to the community, where on-topic specifically excludes "most stories about politics", which is a very easy to bar to clear when the stories you're flagging are literally duplicative of stories with hundreds or thousands of comments on them already.
Because they are long-running discussions, it’s not repetitive. When we allow Rust or JS threads to keep popping up, it’s because we evolve with the topic over time and continuously discuss it.
What the HN shadow mod team is doing is killing the possibility of a long-running, evolving discourse on important topics.
The logic is that people have flagged it, but not enough for it to be marked [flagged], which downranks it. dang, if notified or interested in it himself, could turn off flagging for this submission which would likely bring it back to the front page (given comment activity, age, and current score). You could email him and ask nicely.
You've been on this site for 4 years with 57k karma so you must be very active here, I'm surprised you don't know this yet.
In other words, just because such a system could be used in this way, is it good that it is being used this way? That’s the energy this is coming from.
But I agree with your premise, even in its snark, none of us are stupid - we should already know.