Because it's their original (intellectual property) IP and it is copyright protected, and as long as they hold the license, and refuse to sell it, there's very little that can be done about it.
Anyone starting up a private server for any game runs the risk of a cease and desist letter from the developer's lawyers at any time for that single reason alone.
I know this is a shot in the dark, obviously, but what if the community were to band together, and collectively through email or letters ask NCSoft to sell us the license, they might listen. Wouldn't it be worth it in the long run? It would give those who already work on it here, free rein to do what they want with the game, including monetizing it or parts of it to keep it running, legally. Get a price, do a crowdfunding event, then buy the license. Set up an actual company and brand name. But yeah, like i said, a shot in the dark, still worth trying IMHO.