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.