I have a theory - there's obviously way more pedophiles we're aware of.
The organization may be infested with them top down. If they get rid of all the pedophiles, who'll be left to continue on marrying and impregnating JW women, further passing down the cult from generation to generation?
If they get rid of them, there won't be enough men to serve as elders, and other top positions of slavery.
Another thought comes to mind - induce trauma into the members and you'll more easily be able to inflict the teachings in their mind and put them under mind control. The continuation of sexual abuse may very well be an intentional method of keeping the members under their spell.