Sure there are all sorts of edible flowers but have you actually eaten them? I have, they taste like, well, like flowers. Wouldn't you rather eat something that looked like a flower but tasted sweet? Of course you would.
A good looking cake is worth so much on its own. You almost don't want to cut into it for fear of destroying the design. But man! Aren't you glad you did? There are rainbows inside! The world needs to know.