Electronic signaling is just so marvelously easy to scale that the right path was clear pretty much from day one. We don't have that path for other operating principles right now. As for synchronous operation, binary signaling, and so forth, they're once again just scaling tools that let us crank out designs with billions of transistors without hand-crafting every piece or making the abstractions more leaky than they already are.
Show me a way to keep the network all in optics, all the way through the network - including native positive and negative weights, weights that can actually be larger than 1, and activation functions - without any digital conversion and re-emission.