I think a lot of people just reflexively tack the "noncommercial" clause on there without thinking about it, because exactly as you say, they figure "nobody will make money off my work this way".
The "Share Alike" clause all by itself should prevent any profit abuse, while allowing (for example) someone to charge $0.10 to cover the cost of burning the CD with the creative-commons work on it, or in the case of music it would allow a restaurant to play the work as background music for their guests (but require them to share it if the guests ask for it!).
(To be fair - those cases are arguably not "primarily" about making money and therefore are arguably okay within the scope of the "Non-Commercial" license clause, but that "arguably" part is a big problem in an era with so much litigiousness going on over people's and corporation's Intellectual Precious, so I think most potential users - like Debian - will just stay away anyway because it says "non-commercial".)
If some dork wants to take the game, make fancy new labels, and "sell" copies commercially for $60US each as though they'd written it, the Share-Alike clause still means that anyone who "buys" a copy can legally give out free copies to their friends and everyone else anyway. If they're worried that EA or somebody will trespass on the artwork and they'll find one of the character models wandering around in some unrelated blockbuster game at GameStop(tm) someday, consider that the Share-Alike clause would almost certainly stop a company like EA from doing that, since they hate to share.
And if you figure "but they'll just ignore the Share-Alike clause and make a fortune from my work!", consider that if they're willing to ignore "Share-Alike", why wouldn't they also be willing to ignore "Non-Commercial" anyway?
(In a lot of cases, the "No Derivatives" clause would be a better substitute for "Non-Commercial" with the share-alike clause, I think (i.e. "You can distribute my amazing genius musical works but you cannot incorporate them into the soundtrack for your $500,000,000 blockbuster Hollywood movie"), but that's probably not appropriate here since I assume The Dark Mod developers intend for people to be able to remix and add to it.)
Obligatory Disclaimer: I Am Not A Lawyer, so if anyone reading this is unsure about whether their intended use of a CC-BY-NC-SA work counts as "non-commercial", go find a professional to pay a few hundred dollars an hour to figure it out for you (which is why don't really like the Non-Commercial clause for most uses at the moment...)