Usually there are two buttons "Prev-Next" or something like "Page: 1,2,3,4..".

And I just checked, it's actually just "More". Maybe it's me but it's not immediately obvious that a link (not even a button) called "More" means that you can go to the next page. Add to that that HN is so lightweight I just assumed all messages were loaded at once.

I think people ctrl+F for something and then post a comment "I can't believe no one mentioned X...".

People don't usually reach the bottom of the first page when they go through comments, because the first page is quite big, so they never have to see the pagination (though they do need to know it's not the complete view).

The only thing I can think of is that pagination didn't originally exist, so users could have "learned" that if Ctrl-F didn't find a term, that it didn't exist in the comments (rather than didn't exist on this page of comments). That seems incredibly minor to me, though.

Other sites design their UI to stand out. Paginators may be bolded, or in a different font. And there will usually be other visual cues like a "Page x of y" somewhere. Hacker News' primary color scheme is minimalist grey on grey, specifically so the UI doesn't distract from the content.

As a result, people here develop feature blindness to the point that dang has to remind people that pagination even exists in most paginated threads.