Presumably, a similar ratio was reached for Sydney — although it's Council only began surveying from 1996.
This yardstick does not reflect the actual size of people's enclosed offices. Rather it represents the average space per person that a company occupies — including the reception area, meeting rooms, kitchen, PLUS the enclosed offices and workstations.
As you will appreciate, Office layout design have become much smarter over the years.
However, workspace ratios are principally driven by the general well being of the economy.
That said, there has been a growing trend towards an open-plan layout for offices. And this seems unlikely to change in the foreseeable future.