If this is just another crazy gunman, as opposed to an act of terror or hate-crime, then I'm not saying anything about it except to say that if Americans can't enact sensible gun laws then basically they don't really care about these mass-shootings very much.

So why the hell should anyone else care?

There is a difference between a common-or-garden American mass-shooting versus a hate-crime or act of terrorism. 

I care more if it's a hate-crime or act of terror.

A common-or-garden mass-shooting in USA is a problem due to non-existent or insane lax gun-controls and the crazy gun-culture in America more than anything else, including mental-health. These mass-shootings are inevitable in a society full of guns. Since Americans don't seem to care about proper gun-control, I therefore have little sympathy, apart from for the people directly affected, when this happens in America. It's their own goddamn fault.