I don't believe there is any way that anyone outside of Amazon could truly answer this. The best anyone could hope for would be to guess or speculate, and that's not what this site is about.
As for your comment that "authors selling books in multiple countries could have hundreds of dollars due them", that is simply not correct. The threshold you mention is only applied to authors who choose to be paid by check, and the threshold is only $100. If an author is selling any books in foreign markets, I can guarantee they aren't counting on those sales to pay the bills. Those who are fortunate enough to sell really well in foreign markets will likely have no problem at all meeting that threshold.
Furthermore, if an author chooses to use Electronic Funds Transfers (EFT), then there is no threshold, regardless of where the sales occur. That reason alone is why the vast majority of authors use EFT. If there are any authors who ARE losing "hundreds of dollars", then they can easily resolve this by doing the same.