Mainstream news used to have a near-monopoly on access to events and crime scenes. The advent of smartphones with ever-improving cameras gives the average citizen, who's there in the moment, first access. Twitter just happened to be the medium with lowest barrier to sharing that, but it would've happened regardless. As stations couldn't keep up with the "breaking" part of news, it just made sense (unfortunately) to adopt the share-what-others-say model and talk about that instead.
I don't think eyewitness video is the biggest problem. When @LGBrandon8534932 gets their tweets posted on the evening news and it's treated the same as a statement from Dr Fauci. THAT'S a problem.
Once the floodgates have opened to allow social media statements to permeate mainstream news, there's no limiting which social media is acceptable and which isn't. Eventually, social media itself becomes the news. That feels like a natural progression to me, personally, despite how much I hate it.
