When did the fandom actually start declining? If I remember correctly, it was still going strong during when all the alpha kids got introduced. I think game over and the retcon was when a lot of people lost interest and left? I came in and out of the homestuck fandom, I don't know if I ever caught up with the updates. But as a (recent) archival reader, the game over and retcon did not deter me at all. It was awesome, I loved going back through the comic like a walk through memory lane.

If I recall there was already a bit of a decline by Caliborn: Enter? At least I recall coming in and it seemed like the Fandom had already had its peak a little bit previously, a lot of people actually dislike the Alphas and lost interest because the story pulled back to these new characters after all that happened in Cascade. Even then, the Fandom was still going relatively strong, it was more the Pauses that did it. On two fronts- First, with the lack of updates, some Serial Readers just dropped off, and then, when the Updates started to happen again, a lot of people had forgotten certain points and seemed to dislike what happened next on the principle that it didn’t make sense narratively because the things that put them in context happened like, a year ago.

Time’s another factor here, most of the bulk of the Fandom was Teens. As time progressed, they grew up. Someone reading along for the Trolls and the Alphas in 2010-2011 would’ve spent the same amount, say they are 14 years old by the times the Alphas are introduced. They’ll be 16 when Caliborn takes over the narrative, and 17 during the Game Over update, and already 18 by the time the comic ends. 4 Years are a long time for people to remember thing, and a lot of people are nostalgic of what happened, but either don’t have the time to get back into it, or simply don’t enjoy what they used to enjoy anymore.

Combine that with a negative backlash to the Fandom because whenever something gets too popular means it’s cringey and irredeemable lately, and you have yourself a dropping audience cocktail.