By all accounts, this guy had money, so you can take that out of the equation. He was screwed in the head. Period.
And NO major gun manufacturer sells the device he supposedly used to make it easier to fire faster. It is a trigger guard attachment that is part of the stock that essentially forces your finger to not move like it normally would so that it "squeezes" the trigger faster. Not one serious gun owner would consider owning one of these because they are dangerous.
Guys on the range know using one of these would kill someone because they are hard to control and, frankly, they aren't needed. Your finger will only pull the trigger so fast and these devices are basically snake oil for people who don't know any better.
No, this guy killed so many people because he was well stocked, planned this out meticulously and had a captive crowd essentially pinned in. He fired from a covered, elevated position with no fear of anyone being able to fire back at him. His targets had nowhere to go as they were fenced in and had few exit options. Panic sets in and people don't know what to do, with many, if not most, simply dropping to the ground where they then become still targets out in the open.
He didn't need to have a fully automatic weapon to inflict this kind of damage. If the reports are true about him firing for 72 minutes, then by all accounts he should have killed way more than he did. Most likely he was drunk, high or just simply not well trained in shooting. He most likely just fired randomly as he tried to aim as best as he could, but had no clue how to compensate for all the variables of shooting from that distance.
I am sorry, but more gun laws won't do a damn thing to stop stuff like this. Laws only affect those willing to abide by them and guys like this don't care about laws.