Paul Waldman is right that the media would do us all a service by focusing more on who wins elections than on the expectations game, which is itself largely a media creation. He ends with a pithy comparison that makes his point but also brings to mind some of the larger issues he doesn't get into here:

People often complain that political reporting too much resembles sports
reporting, with the obsession over who's up and who's down, who's
winning and losing. But at least sports reporting is concerned with
actual facts. If the Packers beat the Giants next week by only two
points, no headlines are going to read, "Packers Fall Short of
Expectations." A win is a win.

True. Of course, along with the production demands of campaign journalism (which Waldman details), political (and sports!) journalists--especially those with some space for opinion in their writing--have some additional incentives: at one level they're like gamblers, playing with not straight-up cash but the currency of their own credibility. Pushing the conventional wisdom in an electoral horse race is like taking a safe bet at, well, an actual horse race. Going with a long-shot narrative is a higher-risk, higher-yield thing to do.