Even outside of STF, there's no need for them to be so secretive.

Take Overwatch, for example. If you report anyone, if any action is taken a pop up will appear randomly later when you log in to the game saying "someone you reported had action taken against their account.". It operates on a delay so you can't always be certain who got punished, but they tell you when reports result in actions. This doesn't violate anyone's privacy.