Auto Assault and Tabula Rasa were financial failures. Period. Dungeon Runners was a tiny, quirky, MMO and it simply wasn't making enough money to keep it open. Exteel was closed world wide since it didn't have a steady income in the west or the east anymore and the income it did have simply was just too small.
I don't think that NCsoft isn't totally blameless in any of these games. I'm going off of memory here, so take it for what it's worth, but as I recall, NCsoft laid off a bunch of people including some of the founders from Auto Assault, cutting it to the bone, before the game turned into a financial failure. Tabula Rasa was just kind of a SNAFU all around, especially on NCsoft's part. I mean, I can understand them being upset about Richard Garriott going on his space adventure (and make no mistake, if I had some means to do so, I'd do the exact same thing), but their reaction to it was like shooting themselves in the nose to spite their face. It was just handled VERY badly. Also as I recall (it's been a few months since I researched all of this), there was actually some other company successfully running Exteel in Asia that was paying licensing fees to NCsoft, and NCsoft chose to cancel the arrangement and deliberately kill off the game in markets in which it was doing okay. I can't really speak much to Dungeon Runners as I never played it, but I do think it's a sad day when tiny quirky MMOs are canceled.
City of Heroes was just the most egregious mistake they made, but make no mistake, mistakes
were made with the other games. The biggest one is that NCsoft seems to pick and choose not just winners that they will hype and market the hell out of, but losers that they systematically cut off from any support or marketing, then supposedly look justified in killing later due to lack of interest and/or subscriber base. And not to put too fine a point on it, but marketing and support are the primary functions of a game publisher, which makes them pretty damn bad at the very thing they're supposed to be doing best as a company.