The quick answer is because the comics and video game aren't canon it doesn't matter. The longer answer is I believe the video game happens before Countdown to Darkness, but I could be wrong.
Other way around. Both the game and Countdown to Darkness
lead to the Nibiru mission; however, CtD is presented as a "standard" mission, while the game is kicked off by a distress call (presumably diverting them while on the way to Nibiru from Countdown to Darkness