Gavin Jackson

Chosen answer: Who's to say he didn't later attempt to find him? Wolverine was flung quite a distance away from where Charles was and he didn't have Cerebro with him to immediately locate him.

Phaneron ★

Chosen answer: Yes. But she was already dead in this film.

MasterOfAll

Chosen answer: Because just like in the comic books, all super heroes and villains have names that are a representation of either the abilities they possess, paraphernalia they use, their personalities, and/or the circumstances of their origin. Magneto is a much more compelling and memorable name for a character than simply calling him Erik. Presumably it also avoids confusion if there are several mutants with the same "regular" name, to have a unique nickname for each one.

Phaneron ★

Answer: In addition to what was said, the nicknames also provide the individual mutant a way to identity more closely with the fact that they are mutants. As Mystique said in "X-Men: The Last Stand" when addressed as Raven, "I don't answer to my slave name." Many mutants are rejected by their parents when they find out they're mutants, so the "nickname" serves as a way to distance themselves from those that rejected them. In addition, at times their nicknames are called "code names." In this case, it would be a way to address a mutant without using their real identity, in essence a secret identity that's common in almost all superheroes and super villains.

Bishop73