That's not true. People still pick up USB sticks from the street, people still fall for scam phone calls and people still click on links in mail.

Just because a method was successful once does not mean it was 'burned', none of these people will be checking each and every future pdf or passing it through a cleaner before they will do the same thing all over again and others are going to be 'virgin' and won't even be warned because this is not going to be widely distributed in spite of us discussing it here.

If anything you can take this as proof that this method is more or less guaranteed to work.