The STC report outlines something that has been known and "addressed" as far back as December 2002. A coalition of global aid agencies met in New York in 2002 to draw up guidelines and prevention programs for just this sort of abuse; a larger group reaffirmed their commitment to the guidelines and prevention programs as recently as late 2006. Demonstrably, it has not helped.
Sex crimes are notoriously underreported, and when one throws in the fact that the abusers ARE the enforcers and the protectors, it follows that the victims not only won't report the problem, they have no one to report it to. The creation of a global watchdog agency to police the aid and peacekeeping forces gives a point of contact for the victims, and helps ensure that consequences are swift in coming to the perpetrators of such outrages.