A big part of fandom dis-engagement recently too has been FFN being stupid (ad placement, some algorithm malarkey), and just the stress of the last 4-5 years with mainly the last one being the worst. There's also a lot of guilt or shame in fandom lately because of a desire to constantly be politically engaged, and some folks feel like fanworks take from that. I'm not one of those, but I see it a LOT in my bigger fandoms.
Oh, for sure FFN has been an absolute pain and that won’t help. (Email notifications are terrible; they either never arrive or they get marked up as spam. As for the ads, that’s why I use an adblocker. Lifesaver.) I still use it, but there’s a reason AO3 has gained popularity.
And I am... very aware of the fandom drama, especially the woke olympics that younger fandoms seem to have become drawn into. (I’m really not going to go into it on this post, since there’s a lot of different directions, but let’s just say I’ve seen a lot of drama and it’s certainly very different from the fandom environment I began in.)
As for the last few years... I get it. Trust me, I get it. Since 2016, my anxiety has gone off the deep end (before, I was stressed, but not anxious; there’s an unfortunate difference) so I understand that folks will have been focused on getting through the absolute shit show that recent years have been.
However, I will simply add that all corners of fandom have been affected by the last 4-5 years, including the content creators that have continued to supply the fics, art, gifs, videos, headcanons, memes, etc that have made those years slightly more bearable. The act of creating for creation’s sake is such a wonderfully human thing, but it is still something that requires time and energy, and I think sometimes folks forget that because it appears on our screens for free.