…but that’s exactly what happens on SO: questions similar to an early one are simply labelled as being duplicates, then closed. The only time the monologue is broken is when a new answer to that early (or original) question appears, which is rare.
Not always. From what I’ve observed on SO, a palpable sense of weary frustration tends to appear in comments on “new” duplicate questions (as opposed to “old” ones). The tendency of new SO arrivals to ask first rather than (re)search first is frequently noted (usually adversely) - so far, none of the changes SO have tried seems to change this behaviour.
As for the Haskell Discourse…I myself have pointed out earlier threads on seemingly-similar (or even the same) topics here on a few occasions. Why? Because to me, having a scattered bunch of small threads about more-or-less the same topic appears less “authoritative” than one single thread which contains all of that content (and having just one thread makes all that content much easier to find :-).
Since that includes me, this is also relevant:
…with this presumably being an example: