Not at all. The rest are just not that viable for a multitude of reasons. How many people do Switzerland and Australia have, compared to the US? Much less. And Japan isn't english-speaking, so I dont expect foreign scammers putting effort into learning japanese just for that. They already struggle enough with english.
To be fair, all of that is just me trying to reason through it myself, so there definitely could be other reasons at play here as well.
I hadn't considered the money angle before, but it makes a lot of sense. The poorest US state (Mississippi) has higher per capita disposable income than the 6th highest-ranked country (Norway). Every state other than Mississippi has a higher per capita disposable income than Australia. There are a ton of Americans, they're rich, and almost all of them speak the most popular language on the planet. The US has a high fraction of immigrants (12% of the population), so many Americans aren't immediately suspicious of accents. Compared to other countries, the US is a big juicy target.
1. https://www.statista.com/statistics/303534/us-per-capita-dis...
Also, the most spammed country appears to be Brazil, and it is far from the top of the disposable income lists. Many among the most spammed countries don't register on the top disposable income lists.
There's something else at play here. Likely legislation/regulation.
Spam info: https://www.truecaller.com/blog/insights/truecaller-insights...
Disposable income: https://en.wikipedia.org/wiki/Disposable_household_and_per_c...