Do you know how NDAs work? I'm sure if there's a leak anywhere, they have everyone that's ever worked at blizz with access to that info on speed dial.
Im not saying blizzard couldnt find them if they knew who it was, the cool thing about the internet is you arent there in person and you dont have to use your real name. In fact you can change quite a bit IP, mac address, phone number ect ect. It makes people very difficult to track down, and it makes things like child pornography available, if they could track them down they would (because everyone agrees that shit shouldnt exist), but because no one is dumb enough (except for Dennis Rader) to use their real name and info its virtually impossible to track people down. By your logic you shouldnt be posting on this forum because blizzard could track you down, they have your name, your credit card number and lots more info on you. better watch your back!
What you don't seem to understand is that its not worth it over some dumb game to have your life ruined.
Its not that difficult to be anonymous online. Its also not very likely everyone has left blizzard happy and un-begrudgingly.