YSSY Sun 31/08
One reason - as Missy said - was that there was an "unforecast(?) thunderstorm that swept across Sydney Airport during the early evening"
Just ask the RAAF 34SQN VIP CL60 that taxied for YSCB from Dom5 apron for the 34R MARUB3WOL SID. Passing TWY D they were advised "Taxi for 34L SYD2 DEP due DIV E of COT."
Subsequently, when they neared the TWY A6 holding point for RWY 34L the >24K XW westerly hit with the approaching thunderstorm.
PLAN C: "Taxi to holding point G4 RWY 25" (ie, where you started from, number 8 in the DEP sequence now). By the time they got there again the thunderstorm (and therefore the westerly) had passed through and they had <12K HW. 45 minutes after taxi time, wheels up for the nation's capital.
Add this meteorological event to the numerous staff shortages within the YSSY ATC units at that time - which obviously reduced their through rates (a situation that is ultimately caused by the Australian Government's ATC staffing number employment policies) and you'll understand why your friend on QFA 44 - and tens of thousands of other individuals - were inconvenienced on Sunday.
mmaC