This article from Politico poses some interesting questions.

The notion of the Democratic contest being a dramatic cliffhanger is a game of make-believe.
The real question is why so many people are playing. The answer has
more to do with media psychology than with practical politics.

Journalists, for instance, have become partners with the Clinton
campaign in pretending that the contest is closer than it really is.
Most coverage breathlessly portrays the race as a down-to-the-wire
sprint between two well-matched candidates, one only slightly better
situated than the other to win in August at the national convention in
Denver.

One reason is fear of embarrassment. In its zeal to avoid predictive
reporting of the sort that embarrassed journalists in New Hampshire,
the media — including Politico — have tended to avoid zeroing in on the
tough math Clinton faces.

Avoiding predictions based on polls even before voters cast their
ballots is wise policy. But that’s not the same as drawing sober and
well-grounded conclusions about the current state of a race after
millions of voters have registered their preferences. —Jim VandeHei and Mike Allen