From an outsider's perspective like yours or mine, I see it as two things.
1. Arc has so hyperspecialized into story-rich h-games (a category I've personally never seen a jam for) that it would be relatively pointless to try.
2. Even if it's two days, things like the ear infection mentioned above and other unforeseen circumstances can delay progress on CK updates, thus leaving a different and likely lesser amount of time than allotted for making a game for a jam, either lowering quality of the jam game or of the CK update. Weekly updates are a hard thing to keep up with...
I can't speak for any other devs you follow, or even Arc for that matter, but this is my take on why.