Americans have a most peculiar relationship with their media. Among politically active Americans, particularly those leaning left or right, it's often taken for granted that the media serve some agenda opposite from their own, which explains why their pet stories aren't covered. Conservatives speak of "the liberal media", liberals speak of "the corporate media".

What people forget is that media are first and foremost business, and like every other business the bottom line is the bottom line. The point is not to advance an agenda, the point is to make money, and that means pushing the stories that bring in the viewers. That's particularly true of television, where the merciless dictatorship of the ratings decides where the advertising money flows and which executives keep their jobs.

So a quick answer to "what news stories do media ignore" would be "anything that they think will not grab and keep the attention of their outlet's target audience".