It took a while to find or piece together motives, and to agree on what they were.
There are plenty of motives for the current shooting. Mental problems, depression, suicidal impulses, outsider, family history of anti-social behavior.
Take your pick.
Right, but you said, “They’re called rampage killings, in part, because they do not make much sense”.
They made perfect sense once, once the motives become clear. And that did not take long in any of those case you mentioned.
I have yet to hear law enforcement give a single motive for this event. I think you're talking about speculation.