Instrument ratings
A few facts not included in the discussion.
The weather in the USA is much different to that in Australia. They get a lot more snow and inclement weather compared to us here.
To get a CPL in the USA the candidate has to have an instrument rating or be limited to a short radius from home. I can think that that could apply to pilots going into Ag work.
That aspect of needing an IF rating to become a CPL would surely boost the holder numbers to the 65% that Dick mentioned.
Thirdly to get an instrument rating in the USA is easier because it requires a lesser standard than here. 'Get your instrument rating in 10 days'.
In short the Australian IF rating is more demanding and a better ticket at the end of the day.