The recent disciplinary action against a famous Cardinal for abuse of children and his seminarians has generated a lot of discussion. An article written by a Jesuit priest about why priests don't turn in other priests was insightful.
To begin with, we have to remember abuse and not reporting abuse happens in all kinds of institutions. Penn State, for example, was on the front pages for years. There is a current bit case of sexual harassment in Protestant Chicago area mega church.
The link discusses what we have all experienced working for an institution or even being a member of a family. We feel we want that institution to do well. If one is being abused he/she realizes the institution will be harmed if the whistle is blown. Clergy, especially priests, make a big commitment when they go into the group and if it fails their own investment in it fails as well.