For me it's mostly "fandom x has taken over, time to move on". As in, ignore/leave the comm, or stop subscribing.

But under the current sign-up model that can't even happen. I mean, even if a fandom is recced every month, it is still only one reccer posting for it, unlike the fancake model. And okay, there is no upper limit, so it could be more than four recs, but usually not that many more, and the FAQ even explains that when considering the upper limit, posters should pick something that doesn't swamp the other recs through volume.