I believe it is because they demonstrate the emotion.
I dont know what your asking
Answer:
They are shown in art because art is made to express absolutely everything you want. For example in art everything you use is important because if you are mad you could probably use red or black in your art. Or another is that facial expression and body language can tell/ show others how you are feeling and art is exactly like that. That's why celebrations and rituals are shown in art.
Explanation:
C: Diagonal
Please correct me if I'm wrong!! :)