The ones that get talked about in the news are young, white, men using guns. This is because most of their victims are also white, young, and pretty, and affluent.

Most mass murderers by statistics are not. However if their victims are not affluent, pretty and/or white, dying is somewhat expected.

School Shooters in poor minority schools are routine. Nobody cares.

In addition, gunmen are generally men. Guns are flashy, and make the news, while women killers are more apt at using poisons.

As far as "mass killers" poisoners such as the infamous "Angel of Death" type serial killers rack up far greater body counts than shooters. Generally about 10x as much, as they can often have body counts in dozens to hundreds, where with guns, a body count above 20 is rare.

From the point of statistics, things like school shootings and mass shootings are comparatively rare, but are great at grabbing headlines. As are pretty white young shooters and victims.