It's VERY important this election cycle to remember that the media chooses its candidates not just on ideology, but on their campaign war chests. Much of the money candidates raise goes to the media, after all, in the form of advertisements, which usually must be paid for up-front. Cha-ching! Presidential campaigns are a HUGE windfall for them, so they'll always push the candidate who offers them the biggest bucks.
This extends to their polling, too, of course, in all races from dog catcher on up. They'll make sure they report that the race remains close right to the bitter end, before finally resorting to the truth to maintain their "credibility." The better to get those ad buys from both sides as long as possible.