When Cain summoned Set before, Set could check Cain's status and kneeled down immediately. And now, among the entire demon race, no one else can do that, conveniently.
This reminds me a legendary pot in an Asian food vendor that keeps cooking non-stop for 60+ years. They never extinguish the fire, and just keep adding ingredients and broth.
Someone mentioned already mentioned this above: "perpetual stew."