Because in the setup section the author can talk about the setup. In the pieces section about the piece powers without invoking the interactive diagram which will be saved for the try it section. Of anything the interactive diagram serves both the setup and pieces sections well and it can fit in any of them. But it is more than that by allowing an user to play the game. And currently the setup/pieces section are relegated to explaining what the diagram does.
Because in the setup section the author can talk about the setup. In the pieces section about the piece powers without invoking the interactive diagram which will be saved for the try it section. Of anything the interactive diagram serves both the setup and pieces sections well and it can fit in any of them. But it is more than that by allowing an user to play the game. And currently the setup/pieces section are relegated to explaining what the diagram does.