I had the opposite situation Sat nite on #1586 YYZ-LAX. As recently as Fri it was showing the forward cabin half empty say 40-50 seats available on whole plane. In fact Sat am I changed from 8c to 7c (as 7b was empty). When flight boarded it was packed (2 seats open). Woman in 7b was connecting to SYD and QF only assigned her seat in row 27 at T- 4 hours. She moved to 7b just prior to boarding.
I had wondered why the flight was so expensive in $$ or miles (40,000 miles in Econ).