Because they have to. There isn't enough news to fill the 24 hour news cycle without boring the viewers by repeating the same material over and over and over again. If they only reported the news (the facts and just the facts) they'd be able to do that in maybe 20 minutes (what used to be the length of a normal network news show when you put in commercials.) But now you need to develop a narrative, discuss the narrative, analyze the narrative, etc., etc. to keep people watching and generate ad revenue - because if people tune out after 30 minutes because they just see the same thing over and over then the value of the ads goes down....
If you think this is just a problem of so-called "left wing media" then you are either incredibly naive or so brainwashed by the right that you can't see that the problem exists on both sides.
Whether left or right there's an element of "fake news" in it all - because they're all now at it 24 hours a day and seven days a week and they have to entertain rather than simply inform. It was many years ago that a major American news anchor (from the days before the 24 hours news cycle - might have been Walter Cronkite of CBS or Frank Reynolds of ABC - can't remember for certain) who lamented that the networks no longer valued their news departments and simply kept cutting news budgets in favour of entertainment programming - which the 24 hour news cycle has brought into so-called "news" reporting.