The availability of guns are definitely a major factor. But that can't be the only reason, right? I mean, it's never been difficult to get guns in this country.

There's also been and increase in the willingness to commit these acts

Is it a rise in mental illness over time? If so, is the US unique in this regard? Because I don't think mass attacks (shooting or otherwise) occur in other countries at this frequency. And why would mental illness be increasing?

Is it media coverage (and/or social media)?The fact that someone can instantly go from unknown to world famous.

Something else?