Why do we have so many mass shootings outside of terrorism these days, anyway? Definitely a problem of today.
Well, one way to think about it is that
generations of "TV culture" have replaced community, while extended family is less of a thing as well. Another important fact is that people
talk much less to friends of any type, than they did 50 years ago, and it's not just the internet that did that, it started declining in the early TV era. All types of community connections between individuals are much weaker than ever, and it's been replaced by the mass-media TV "glue" to hold everyone together instead. The internet isn't a panacea for that problem, either.
You are dissociated, disillusioned and nobody hears you in such a culture? You have to do something fucked up enough that the media is going to sit up and listen. You're not nobody now, you're somebody, even if that somebody is hated. You're talked about.
Also of note is whether there were random mass-shootings
before you'd be immortalized on TV for doing so. While there an army veteran who did a mass shooting in 1949, they really didn't start happening among young people until ~1966, which is well into the TV mass-media era.