The characters have been powered down just like the X-Men Movies. Jean Grey could fly in the comics, but couldn't in the Movie until she became the Phoenix. Or Magneto, in the comics, could create a Forcefield that protects him from all incoming attacks, but he couldn't do it in the Movies.
In the game Johnny Cage, Sonya Blade and Shang Tsung all could throw different types of energy attacks, but couldn't in the Movies. Games, Comics and Movies are all seperate entities. Just because they are able to shoot Fireballs in one medium, that doesn't automatically mean that they can do it in every different incarnation.