By experience, since I have lived outside the US, others can relate too. In the US you tend to live lonelier and have less social interaction with others. Perhaps one determining factor of so many lone wolf killings might be that too. Less social interaction, less sense of community in many areas.
In Latin America and Europe where I have also lived, you don't have that. But you still have people with mental issues in any case. However, having more people around you, interacting with you helps.
This problem needs to be seen for what it is, if not like I said it will only get worse. Already politicians are dancing in top of the graves of these children asking for more power, and ignoring that guns don't kill people. People do. Yes lets have a sensible discussion of having people with mental issues without guns or weapons that kill, but going after guns will not fix it.
The same way that gang killings isn't solved by tougher gun laws, these issues of random killings won't be solved if we don't go to the root.
Guns don't kill people, people do. In the USA at an alarming rate, in every other developed country at nowhere near the same rate. I'm not suggesting we ignore other issues, but you cannot simply ignore that this problem does not afflict these other countries anywhere near as much, despite having a lot of cultural and societal issues. What's wrong with looking all avenues for reducing the problem? Look at what works for others and adapt them for the USA.