In reporting out a story, it is the journalist's responsibility to obtain factual and verifiable information. People are the center of the story, and using their real names adds credibility to the story.
Now, there are circumstances where reporters use pseudonyms for sources -- mainly to protect victims of sex crimes -- or anonymous sources entirely. The latter is constantly debated among journalists. However, the consensus is using anonymous sources is necessary when all other avenues of getting someone on the record is exhausted or the story is so explosive that people close to the information are willing to shed light on an issue so long as their name is not used in print, mostly from fear of retribution, which is more common than you think.