What the hell is a “non-political mass shooting”? Columbine wasn’t “political”, it was a couple of assholes who literally just did it because they thought it’d be ‘cool’. They didn’t make political demands or say “this is because gay people have rights” or whatever. You hear about more mass shootings in general starting around Columbine for the simple fact that that is when mass media and the Internet were becoming established.
But there were mass shootings before that, just because they didn’t go viral on non-existent social media doesn’t mean they didn’t happen. The whole reason Europe has the modern gun laws it does is in no small part because they’ve had mass shootings of their own.
You’re trying too hard to try and pin this one on the US and the more you try to defend the notion the more clear it becomes that this isn’t about shootings, it’s about some kind of weird agenda.