Without seeing the art, I can think of a few explanations.
The artist is drawing a concept, say an epidemic/disease, as a monster to make it easier to communicate. From what I understand aincient art is often very symbilc, which would fit this very well.
Propaganda, the ruler wants art that shows them as powerfull, strong, and fighting/killing a sky monster is a powerfull message without angering neighbouring leaders into a real conflict.
Fiction/immagination, today works of fiction are very common, so why not in the past as well? Someone painted something just because it looked cool, is that so unresonable?
Also, pointy roof make rain and snow fall down better than non-pointy roof.
Also, monument point up, because making monument point down makes it fall over.
Without seeing the art, I can think of a few explanations.
Also, pointy roof make rain and snow fall down better than non-pointy roof. Also, monument point up, because making monument point down makes it fall over.
The more things change the more they stay the same.