beyond the press releases by politicians, police and corporations, the mainstream media has been getting a not so insignificant amount of their news stories from social media for over 10 years now. this isn't just in america, it's worldwide. citizen journalists on twitter have been the ones to point out things thats have made headlines around the world.
those legit sources do good work with investigative journalism but they build on what they found on twitter and other social media sites.
in fact we know those legit sources you want people to go back to have historically ignored many communities and similar news stories decades prior. they report on it now because they know it's what people are talking about without their contribution.