I've written a lot of fics for /co/ over the years. It's indeed been quite fun.
I guess I would say that what's holding us back right now is that, frankly, we don't have one good, big new thing that's sucked us all in. Wolfbatman, for example, came from the extremely high-energy moment of Sozin's Comet and The Dark Knight coming out at the same time, and the entire board watching both. /frz/, and all its creativity, sprang from everybody watching Frozen because it was such a phenomenon. Ideas, fanart, and fanfics spring from the energy of a lot of Anons on one hype train, and it feels like we haven't had a single show or movie or comic that's generated that in a while.
There's also the fact that, as mentioned, some of us moved on to other things. These days I mostly write original fiction and poetry; my fan content days seem to be done, outside of individual pastebin stories here and there.