thing is directed graphs have loops in them, but I'm a bit unsure what it would mean to plug the output of a blob directly into one of its inputs. for instance suppose you had \$$\Phi : X \nrightarrow Y\$$ and \$$\Psi : Y \nrightarrow Z\$$ – you could tensor them to give \$$\Phi \otimes \Psi : X \times Y \nrightarrow Y \times Z\$$ – and maybe if you "loop" by plugging the output \$$Y\$$ into the input, you'd get plain old \$$\Psi\circ\Phi : X \nrightarrow Z\$$? but I'm just speculating here.