I tried to explain that above, and linked to past explanations of the same points. If you want to take a look at those past explanations, and still have a question that isn't answered there, I'd be curious to know what it is. Perhaps it would be helpful to describe what these links contain more explicitly:
(1) We try to optimize HN for intellectual curiosity: https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
(2) Curiosity and repetition don't go well together: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
(3) With submissions on a MOT (major ongoing topic), the main thing we look for is SNI (significant new information): https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
As far as I can tell, the complete answer to your question follows from those three points.