Just out of curiosity I checked flights to Cairns from Adelaide. Jetstar have the only direct flights and as Virgin is the AFL carrier I guess a stop over was inevitable.
Though one stop via MEL, SYD or BNE can be had all on the one day. Overnighting has to be a lot more stuffing around, than just transiting through on the same day.
For example next Thurs (so I assume yesterday would have been the same):