It's like how they say certain intro classes for majors are difficult to weed out students who would eventually drop out if they reached harder classes. The logic there is students aren't wasting their time taking classes they won't use when they switch majors, and the classes won't be filled up before students who will make it all the way can enroll.

This way the scammer isn't doing a back and forth for 2-3 emails with those who would eventually realize its a scam. They immediately weed them out so they are spending time on those who will payoff.