Firstly, rioting isn't that common, at least not yet. That it seems to be becoming more common indicates people are finally snapping out of their apathy and taking action even if it is, at the moment anyway, often compulsive and self-defeating.
I don't think solemn promises made by news media types and politicians are taken very seriously by the demographic they are aimed at. How often does a public official solemnly swearing to rectify x, y or z, actually translate into action and meaningful changes being implemented? As for "trusted" news anchors...they are basically just teleprompter jockeys with no real resources or power to do anything other than, well, read the news.
Lastly, as has been discussed, journalism is in the midst of a metamorphosis and investigative journalism isn't a priority for mainstream news organizations. The few journos that do stick their neck out are often harassed, or worse, by the TSA/NSA et al. if they start getting too close to uncovering facts that threaten the status quo.