Predicting Flaw in users action and giving feedback to user

Recently when I was using Gmail i ought to notice that Gmail runs an algorithm by which if user types " I have attached " in a mail and does not actually attach mail it shows a dialog confirmation asking "it seems like you forgot to attach file" which is actually a very good experience keeping users in a mind . Google may have done a lot of research about this surely. But why limit it to just one sentence prediction. I tried Using "PFA" "Attach" "Please find attachment" but I never saw a dialog in this case. what may be the use-case for this?