This is why it happened. Mystery over. 99% of the time, "we didn't do nuffin" means that the site's moderation was not as tight as once thought. Ignorance isn'

This is why it happened. Mystery over. 99% of the time, "we didn't do nuffin" means that the site's moderation was not as tight as once thought. Ignorance isn't really an excuse on this, because it takes five minutes to explain to people nofollow vs. followed links. However, when you explain it to people, 99% of the time, they will continue breaking the rules because they have time preference issues: they know that they benefit from their site passing rank in the present, and the penalty is an unknown quantity in the future.