First, people have fundamental drives that can override logical reason. Gift cards probably aren't your button. Maybe your buttons aren't even ones that are easily poked at by e-mail, I dunno. But EVERYONE has buttons somewhere that make them exploitable, and a lot of them ARE e-mail accessible... maybe as easy as offering free money, which is a pretty common one, and it's why marketers have been obsessed with it for ages.

Another factor is that a lot of people have jobs where they're really busy and deal with a lot of e-mail from people with all kinds of bizarre communication styles. Catch one of them with the right e-mail on the right day, and you'll get a careless click.

Black hats get to try every day across lots of people, and they only need it to work one time against one person to score.