The perpetrator in events like this is almost always written off as "crazy." Often the purpose of that is to dismiss the premise that any systemic factors may have been at play. If he was just some random loon, there's no need for the society that created him to examine itself, much less attempt to resolve its own issues.

This is what a lot of people are afraid of in the US, because these shootings exist at the nexus of first and second amendment rights. The first allows people like the shooter to be radicalized using the most powerful communication platforms ever created. The second allows them to be armed to the teeth. And then there is the systemic, deeply rooted racism in American culture that feeds the hatred behind these events, and intersects with the US Constitution, government and society in numerous ways the country still isn't capable of discussing rationally.

So "he was just crazy" starts to sound like "nothing to see here" after a while. Because if it's true, it's weird that so many people seem to be crazy in the same way. If they aren't crazy then there is a pipeline of radicalization and violence - an "extremist industrial complex" if you will - that's working as intended to maintain its own status quo... and a lot of Americans are fine with that.