Newspapers and news outlets aren't actually "primary source". If you read a quoted tweet from Obama in the New York Times, the NYT isn't the "primary source" - Obama is. The NYT is a secondary source that is quoting from primary source.
In that sense, Twitter is actually primary source, because Obama wrote the tweet. Well, except when Twitter is hacked, which is what makes this such a significant event.
(But I agree with your general comment, especially having been interviewed a few times and seen how most reporters work. There are a handful of good ones out there though.)
Or it could be the result of a decades long effort to attack credible authoritative institutions by forces that take a dim view of transparency and accountability.
If 200 people on Twitter are angry at politician X over something trivial, we are served a news headline of Person X accused of Y - Public calls for resignation.
An anonymous person on social media recently made a claim of sexual assault against Justin Bieber with no evidence whatsoever, and the media reports it as Justin Bieber accused of sexual assault. He was fortunate to immediately whip out numerous receipts countering the claims, but what if he couldn't? We would still be reading headlines about this baseless accusation.
This is largely through their own actions. Examples are legion, but a recent one is debacle at NYT over an op-ed. The news-consuming public was able to view the shenanigans of NYT reporters and staffers, which would formerly been done being the scenes.
Many eyes were opened, and I'm certain I wasn't the only one thinking "These are the people in supposed to be trusting for my news and analysis?"