For that matter, why the optocoupler at all? You only need it if the systems are at different electrical potentials, and even then they are galvanically isolated on the Pis by the magnetics in the Ethernet.
But I guess it's not the same as being asked "where's the air gap" pointing at the optocoupler, and saying "there it is"
But I guess it's not the same as being asked "where's the air gap" pointing at the optocoupler, and saying "there it is"