A 60,000 seat stadium with no GA standing room will never get to a 60,000 crowdie corporates who have to pay, but get 10 seats or 15 seats or 20 seats for their boxes and not everyone rocks up would make up most of that 400+ shortfall. Illness and accidents, maybe even a death or two would see some punters who have paid $150-$200 of their own hard earned not make it to the game and not give their ticket away to someone.
The MCG only gets over 100,000 at the GF sometimes is because they sell more than the 5000 GA standing room tickets because if they only sold the 95K seats and 5000 standing they would always fall below 100,000 due to the various reasons people end up not showing up..