People may like what third-party candidates say, because often they are the only ones saying anything, but they usually won't vote for someone who doesn't have a chance. Since third-party candidates are not in the news, they are considered to be not really in the race; and since they are not in the race, this justifies treating them as if they are not news.
The first sign of corruption in a society that is still alive is that the end justifies the means.
Life's not black-and-white. Sometimes the ends justifies the means.
Journalism justifies its own existence by the great Darwinian principle of the survival of the vulgarist.