Although no Airbus document gives the reason it is true that they have submitted for certification that all abnormal landings will be in CONF3. It even goes to ridiculous extent of selecting Conf3 for approach when flaps are jammed where you only move the flap lever to 3 when nothing else moves. Flap full is mostly drag and for any situation like wind shear, gust etc. CONF3 is preferred. It gives better handling and control so why not in abnormals? Go around in many abnormals require configuration to be maintained which will be problematic in flaps full.