One word-geometry. Thats why they come together. The collision was inevitable once the PIC started to follow the 18A lead in line. Why he/she thought that line was the correct one is the why that should be looked at whether its Qantas Safety or the ATSB. As it involved Qantas aircraft at a Qantas terminal and doesn't really have any safety benefit for anyone else other than Qantas why would the ATSB be involved? I imagine that the safety outcome will be an some form of internal communication for pilots to be more familiar with the configuration of the bays or that they stop using Alpha bays altogether.