I saw a comment on Tumblr that this Korrasami ending was the ending we all wanted, but that we weren't emotionally ready for it. I think they're on to something; we did all want it, but we weren't ready for it, because we didn't think it could happen - it was our impossibility.
But suddenly it actually happened, and the world changed, and we're all in a kind of shock from the emotional unreadiness. It's the best kind of emotional unreadiness, perhaps, but unreadiness nonetheless.
I think that comment reveals a lot about why so many of us are reacting not just so strongly, but over so many days. We weren't ready for this; we couldn't be, because it was impossible. And all these many days of reaction are us emotionally processing that the world is suddenly new. Particularly for the adult fans, we're... catching up. We're playing forward this emotional release from all the years ago when all the straight kids got this sort of thing but we didn't, reeling it out to whatever point our adult lives are in now. That takes time. It may take a lot of time for some of us; it's as if a lot of very old metaphorical/emotional logjams across the many people of the fandom have been blown clear, and it's all cascading downstream.
The poison wasn't just in Korra; it was in a lot of us, too.