Heads up Plague speculation below!
I'm having the most big brain take right now, what if plague isn't covered in some weird meat but rather it's all a fungus?
In nature (not the flight) there are plenty of fungi that imitate flesh and carcasses to attract flies, bugs, and whatever else to carry their spores and stuff far away or to other fungi for reproduction, and there's fungi that infect insects too!
So it wouldn't be far fetched to assume that the wyrmwound and all the little dips and bulbous shapes in plague would contain a goo like that meant to attract insects.
The reason the Gladekeeper is enemies with Plague is not purely because it's the whole life/death thing but rather because fungi aren't plants (biologically speaking).
She can't control fungi like she can with plants, they don't grow how she wants, and while it's not an issue with your fly amanitas and chanterelles it'd certainly be an issue if the fleshy mold of plague were to let loose over there.
The flights neighbouring Plague aren't in direct danger as none of them are particularly hostile with plague, or have certain natural defenses.
Arcane is already irradiated with pink stuff and would destroy any non native life trying to survive in it's soil in an instant, Shadow seems to be able to control fungi and convert them as shown by the border between their regions:
Those mushrooms look very similar to the ones on plague's side, except shadow-ey.
Earth is a rocky wasteland, there's hardly anything there worth growing on and infecting, and Wind probably blows away the spores also why fight the Windsinger he's a friend.
This is also why mirrors can't just chomp the ground and eat the flesh, because it isn't flesh at all, they can't process it!
