I think you'll find it's more to do with regarding Australia as a "mature market" from a purely marketing point of view.
Several reasons:
1. Market saturation:
There have already been significant sales of detecting equipment into the Oz market, much of it in recent times, and much of that recent-technology gear is now circulating in a large and mature 2nd hand market.
2. Demographics:
Like so many other physical outdoor pastimes, gold fossicking and treasure hunting are becoming a bit passe with the Western younger set, who would rather spend their "activity" money on paragliding, wind surfing, dirt-biking, adventure hiking, and boot camps and gymnasiums.
3. Opportunity:
Oz, like so many other western countries, is increasingly placing restrictions on activities that are seen as not being eco-friendly (and I don't want to buy an argument here).
I have personally experienced this sort of thing in the never-ending efforts by some to eliminate trout as a species in Australia, on the basis of their effects on some native species.
4. Gold - or the lack thereof:
In terms of gold freely and easily available to the part-time recreational fossicker, I think Oz is increasingly seen as "been there, done that".
Yes, some people are still finding good gold - but have a look at the reward-for-effort ratio, and remember the 80/20 rule discussed recently in another thread.
5. Economic security:
In a country like Oz, where people generally have a well-paying (?) job, urban and health infrastructure, and a myriad of other recreational opportunities. there is less incentive to pursue gold as a source of economic well-being and security.
So, effectively, the African/Middle East, and other markets, represent a less regulated, younger, economically aspirational market.
They are also, in general less educated, and less experienced in their purchasing decisions, and hence more susceptible to marketing terms like "easy expert" and "All gold. All soils. All the time."
Most seasoned prospectors, such as those found in a more mature market like Oz, would want to see a lot more than that before parting with the hard-earned.