If Toll etc were to start operating out of YBAF I would expect a large horde of residents with pitchforks and flaming torches to turn up shortly after the first flight. There are enough noise complaints about Cessna circuits without chucking a bunch of night freighters into the mix. At least YBBN gets them off over the bay most of the time; Archerfield is surrounded by houses. Brisbane's shiny and upstanding freighter fleet
is most active between 2300 and 0330hrs, hardly conductive to good community relationships.
The second problem with moving freight to BAF is its lack of ILS. Freight businesses trade on their rep for getting freight from A to B in any conditions. If they have to divert to ybbn every time it gets cloudy, they may as well stay there.
The third problem is that a certain amount of freight comes in on jets and gets transferred to metros (and vice versa). When they all nest at the same airport that's really easy, but if the metros went to BAF it would all have to be trucked to and from Ybbn. That adds to time, cost and lost-stuff enroute factor.