are piggy banks shaped like pigs because its a metaphor for the greed of capitalism
Actually it’s a pun.
Way, way back when English was a simpler language, the people used to save their spare coins in containers made of really cheap clay called ‘pyg’.
It wasn’t long before someone thought of the joke of shaping them like its phonetic counterpart. Though early models didn’t have the holes in the belly for the cork and, if you wanted access to your saved change, you had to “break the bank.”