It's not self-professed candidates. It's what I call "mentionables." Some are actively campaigning already (R. Paul, H. Clinton, C. Christie, etc) and some are nowhere near that and many never will. Mentionalbles become actual candidates and get a "dot" next to their name when they explicitly say "I am running" or form an exploratory committee or something similar. Mentionables get struck when they explicitly say "not running." Then there's the special cases -- those that get struck because I happen to think that they'll never run due to significant events that intervene, such as losing another election in the meanwhile or becoming embroiled in scandal quagmire. These people may not even realize themselves that they won't run, and that's the class that C. Christie falls into. Others who will never run for anything ever (D. Trump, T. Nugent) don't get struck because their jokiness deserves recognition.
To reiterate -- in my opinion C. Christie will not run for president. He may not even serve out his current term as governor. It's funny to see him out there doing his dance while the curtain is already falling. I'll admit, he had a good thing going before his ham-handed political brutality alerted the world that he's a generator of massive corruption, New Jersey style.