One guess off the top of my head - Limiting to US is a quick way to screen for writers that have experience in US English (which their clients expect). It's n

One guess off the top of my head - Limiting to US is a quick way to screen for writers that have experience in US English (which their clients expect). It's not perfect, but it does a good first pass of removing individuals that speak different dialects of English. One big bottleneck for this service is the editing/grading - so reducing the time spent on that task is essential if you are trying to make money.