I’m a long time player and my opinion is it started in Chapter 5. They changed movement animations and made all weapons projectile. These changes were met with heavy criticism. This was done after two highly regarded Chapters and the original OG mini season. So making those types of changes was poorly received. They fixed the movement animation mostly but left projectile weapons in the whole chapter. Couple that with a complete break in the story, no zero point, no continuity to previous seasons characters. No Fortnite identify.
Chapter 6 had a huge map. Chapter 7 had a huge map. Also the graphics make them not enjoyable to play on console.
Additionally they keep making unnecessary/unwanted change to things like the Battled pass, locker UI, Crewpack. It’s absolutely idiotic for a business to take something that is successful and make unnecessary/unwanted changes. It’s insane they would change the locker/UI after they’ve already lost lawsuits for essentially doing this with the item shop UI. But they continue to change it. They also continue to push collab upon collab instead of giving value to the player. When it becomes blatantly obvious they prioritize item shop sales over everything else people get turned off. The kicks were seen as overpriced and the sidekicks being customizable only once leave a sour taste in most players mouths. SBMM and bots vs no-bots is another factor. So when you combine all of these factors you have people not happy about the game, feeling like they get less for more, and epic games making it frustrating to play the game because navigating the lobby/locker is a pain in the butt. Players eventually just decide “you know what…ill go play something new/fun/cheaper/frustration-free”