Because easy scams to detect prevent false negatives for the scammer. If you get a response to a badly written scam, chances are the respondent will be a sucke

Because easy scams to detect prevent false negatives for the scammer. If you get a response to a badly written scam, chances are the respondent will be a sucker and the scam will be successful. If you get a response to a hard to detect scam, chances are you will spend more time for a less likely payout. Microsoft wrote a paper on this. The same reason email scams are so bad.