I heard there is this weird statistical phenomenon where as the scammer, you actually benefit from the email message being a little bit dumb. If it were actually a plausible message without typos and obvious red flags, you'd catch many more skeptical individuals in your pipeline. You spend time trying to get these people to send money, but eventually they inevitably realize it is a scam, and your time is wasted. Extremely gullible people however, won't be deterred by typos and red flags. Therefore, typos and red flags filter out skeptical individuals, enriching your pipeline.