Because in ZImbabwe (and other African countries, no doubt), many men believe that having sex with a virgin can cure AIDS.
"Like many young girls in Zimbabwe, Hope was the victim of a widely held belief that if a man with HIV or AIDS rapes a virgin he will be cured of his disease. This so-called virgin myth, perpetuated by Zimbabwe's traditional healers, has led to the rape of hundreds of girls, according to UNICEF. Some of those victims are too young to walk, much less protect themselves."
Condoms really won't help here, will they?
Betty Mokani, who was raped as a 14-year old by her uncle, started an organization called Girl Child Network Worldwide, to provide a haven for the tens of thousands of girls who are abused in this way.