If you mistype someone's email address or inadvertently send it through someone's domain, you can be placed on a mailing list that is sold to email spam houses. Again, this acts to generate traffic to a specific site. Most people are unaware that their typing carelessness can translate into profit for these pirates. Taking advantage of this natural occurrence, typo pirates are essentially leeching off another site's success. It is a huge business and it works.
Traffic is the bread and butter of any site.
The higher the number of visitors, the more profit or advertising revenue you can generate. It can also be used to get an edge on your competitor. Then there are those who go straight to the source to steal names. Because of loopholes in registration security, they can contact your registrar and effectively transfer your name to their possession. By faking their identity, they can steal your name.