The most prolific one I keep returning to I’m not sure really counts because it never had a full fandom. Dino Run by PixelJam was very popular when it came out (2008?). But aside from a few fanart pieces there was never any fanfic. So I would have this cycle where my brain would be consumed by this game for 1-2 months and then go dormant for 2-3 years. Every time left sad/disappointed that there was never any fanfic for it. Then in 2021 I was finally inspired to write for it. Only 2 people who have played the games have read, everyone else has been fandom blind lol.

Any of Minekura Kazuya’s work. But purely for fanfiction as I have never meshed well with the artists nor general fandom. Her work while very pop also has a lot of emotional density so whether I want to or not I have to take years long breaks. But once and a while whether I’m updated or not on her stories I will check out what is out there fanfic wise. I’m usually not there for long because the most popular dynamics are not the reason why I read her works.

(will think of other examples later but these are the major 2 to come to mind)