Because Rebecca Romaijn Stamos is running around blue and naked (save for prosthetics) for her part in the movie?
And then, of course, the part after the cure when she is no longer blue but still naked
I think this movie could have been a little bit longer, but I didn't mind all these "appearances". I mean, after all, having to independently develop EACH character that ended up with Magneto would have been a bad idea. His little resistance force didn't need hundreds of individuals, it needed a collective unit to do some neat looking stuff and then get owned.
I never read the comics and I can't remember too much of the show, but I was very pleased with what I got for my $8. More time would have DEFINITELY been helpful. I think, unfortunately, this and all comic book related movies are set-up to disappoint those people. I don't ever foresee a comic book movie going too long over 2 and a half hours, and regardless of what series, that is simply too little time to allow for being able to get everything accurate. Especially with really involved storylines. For example, Spiderman 3. Last I heard, that movie is going to have Venom as one of the villains. From what I've heard, the Venom backstory ALONE could fill at least that much time, if not more.