The only reason I can think of that V/Line's purely use the old BG platform - platform 2 - is that during the gaps between services the train is out of the way of main line traffic.
I was also surprised to learn of how great the platform-train gap was woodford! I knew it was a long stretch up (even so that the conductors regularly mention it upon arrival) but would never have guessed it was upwards of 30 cm.
I think you will find the back platform track belongs to Victoria not NSW, which is why they use it. It was relaid using second hand BG sleepers and something 110lb rail, ie all second hand Victorian material so it did not cost them much.