Remember that any god or angel who breaks the compact and enters creations, by the power of the compact itself, will be made mortal and vulnerable. The exception being Hyborem, of course, given that he used sneaky methods (if I'm remembering dismembered bits of lore correctly). I doubt Agares would want to risk his existence when he can continue his master plan via minions. Same goes for the other gods, I would think; although it might make sense for one of the more benevolent ones to risk it all in an attempt to save what's left of humanity.
Er...of course, there's still plenty of humanity left, given that Armageddon does so little...