Mass shootings are shocking. However, realistically speaking, the number of people dying in gangland wars etc. is even more shocking.
The problem with covering those, is that it highlights a part of minority culture that a lot of members of minority want to detach themselves away from. On the other hand, not covering them seems like you're putting an emphasis on white people's problems, and ignoring problems of minorities.
You can't really win when it comes to covering gangs consisting of demographic minorities and their criminal behaviour. It was the same with the Mafia. Italians would get defensive about it, and thus the Mafia went under the radar for a long time, partly enabled by the "good, hard-working Italians" who didn't want themselves to be shamed by being associated with a criminal group.
America's demographic majorities are in a better position to be self-critical and self-evaluating about the problems within their group, thus they often end up receiving a larger emphasis in the media.