I don't understand what can be so hard about "supporting" more countries? It's the internet. Anyone can access your servers. International credit card charging was invent decades ago. Take my money.
Probably that fraud detection doesn't work well enough in some countries to make more money than you spend. AVS, for example, is only available in the US, UK, and Canada. It sucks, but for some types of services, there's an army of people trying to use stolen CC numbers.
Not speculating on why, but yes, those are the only countries that do AVS. Though AVS is just part of it. They support Singapore, which doesn't do AVS. So apparently whatever fraud protection is available there suffices.
Also, it's available in New Zealand, but not Australia, which is a fairly large anglophone population.
