Well it comes down to gamers voting with their wallets. TR was clearly rejected by the market as was AA. (Dunno about S&B)

Although I do think NC is quick to pull the plug on things there is more to this them subs. Spaceman Spiff err...Richard Garriott promised NCSoft the MMO to end all MMO's with TR. There was much drama right down to Rich deciding to go on dispite the fact NC Korea didn't like the game's design direction and chose not to launch it in Korea way back when.
Now Rich mysteriously desides to pursue other interest...(no, they asked him to resign) and I'm telling you, the last thing they were going to do is keep a game with his name plastered all over it after he cost them 74 million dollars making it and the game hardly sold at all.