Nostalrius Begins - Quality wow vanilla realm (1.12)

From a legal or financial standpoint, how can this server being around hurt Blizzard? I understand Nostalrius is using their game but it hasn't been for any financial gain at all. The only money I see trading is with gold sellers, and that is against Blizzard's own rules but that is the only thing I can see here that would cause for them suing.

I'm sure I am missing something but I am not sure what. It's a free to play no profit server.

Blizzard mad becuz the server starting to eat into its subscriber base in China.

And because they have been butthurt at the shit state of their game since panda-land and, to a lesser extent, destroy-all-azeroth came out.

"OH TEH NOEZ!!!11 TEIR SURVURR BETUR EXPYRUNCE!!11!1 SHUTDOWNSHUTDOWNSHUTDOWN!!!!" -Blizz