There are A LOT of applicants who indicate they're willing to go anywhere, so those people are filtered into the countries without as much specified interest. Last year they had 23,000 applicants for less than 4,000 positions, so there is no reason they wouldn't be able to fill a group. South Africa is also a regional medical hub, so many applicants with medical issues end up being placed there. South Africa also has an application deadline of July 1st, so many of the people who will be under consideration likely haven't even applied yet. Lots of applicants don't hang out on the message boards either.