Because (a) by the rules of engagement, management is not required to share original feedback, and (b) the original feedback could be used to identify the sources. In this case, there might have been a real risk to the sources given the individual in question is known to mobilize internal and external forces like Twitter mobs to personally attack people and bully them into submission.

I think this argument would stand on its own without the very specific claims about the person in question, which are a little strong unless you have personal information.