I think the only reason of why it works is that Ukrainians are an even lower trust culture, and they are better and more cynical at duping people. Plus, in Ukraine many people see it as their patriotic duty, and perhaps rightfully so, so these kind of jobs are likely to attract quite sophisticated people who will be able to pull off very believable scams, not some social rejects or worse, forced labor sitting in Myanmar jungle, as it is in Asia vs USA scams.