I believe the crew had plenty of gas - were in no trouble and being OOL locals knew the amount of traffic going in and out they would disrupt once they did a wheels up. They seemed to wait until the bulk of all the arrivals and departures had finished, and by the time they did it - only the last 2 JQ domestics and the one from WLG was due to come in. I think in the end only only JQ flight diverted to BNE, the other held and got in after they picked it up and cleared it off the runway. Gave the emergency services plenty of time to get stuff ready as well, and in general less fuel the better I guess in this sort of situation.
I agree if you need to do it, stuff the ramifications, but it holding for another hour or 2 doesn't disrupt the entire industry as much, reduced your weight, why not wait.