I don't see what you mean - you have fixed taxes at:
AU [Passenger Movement Charge] AUD 47.00
IA [Passenger Security Charge] AUD 12.90
WG [Safety and Security Charge] AUD 7.97
WY [Passenger Service Charge International] AUD 41.00
YQ [Fuel Surcharge] AUD 144.00
and then add the fare component which is the same both ways (in the same fare bucket anyway).
Unless you mean why the taxes differ - BNE charge more for departures than WLG (of course not factoring in the NZD25 departure fee paid on departure at WLG).