Since the days of Charles Taze Russell, the Watch Tower Bible & Tract Society has made the claim that Jehovah's Witnesses are the only pure religion. They have taken shots at many religions, especially the Catholic Church, including pointing out the various scandels that plague religions. In addition, they claim that their organization is a spiritual paradise.
So, to prevent making themselves appear to be hypocrits, they must hide the childe abuse within their ranks. The WTB&TS, especially under Rutherford, has gone to great lengths to make Jehovah's Witnesses stick out from the rest of the world's religions. Although the right thing would be to out the violators to the propert authorities, it would damage the image they are attempting to portray.
It would be a better Witness to assist the authorities in the prosecution of these vile people. However, that would still mean there is a problems with child abusers inside the organization.