Re: fandom fic conventions, VERY early FFN work (like...2000-1) had huge gigantic chapters, sometimes even having one chapter with multiple headings (chapter 1, 2, etc.) inside it. So I think maybe it dates to when FFnet had different formatting? And you could be on the money with your guesses as to FFN's front-page listings. I also think that FFN was dominated by teenagers for a very long time, who aren't known for their pacing abilities.
All of this makes a lot of sense! It’s eternally striking to me that ArchiveOfOurOwn will regularly feature stories that have like 20,000-word chapters (which personally drives me nuts because it’s so hard to keep track of where I am in a story) whereas Fanfiction.Net will often have these teensy chapters that are 500 words each or something. FFN will often feature 5+1 stories where each of the six micro-scenes is its own chapter, and AO3 pretty much never has formatting like that, with people almost always putting the entire list fic in one chapter.
Not gonna lie, I’m glad I missed the era when FFN had super-long chapters. I always always prefer reading stories with shorter ones (although maybe I’ve just been trained that way with everything from James Patterson novels to drabble collections online). I do so hope that FFN continues to update its formatting into the future, because right now their formatting conventions make me tear my hair out every time I try to upload a fic or chapter there.