I have no idea on a metric of how frequently an “ordinary” gun jams, much less these modified ones, but I can apply some logic from my knowledge/experiences. The weapons you mention having experience with are designed with appropriate tolerances to not bind up under heavy use, so are a bit different from the ‘consumer-grade’ type we’re talking about in this specific event.

The type of semiautomatic rifles we’re talking about here use recoil to cycle the action. A bump stock allows the whole weapon to oscillate - and can have an effect similar to not securely shouldering the weapon. This prevents the needed energy from being transferred into the action for complete cycling, and that would make the weapon prone to jamming.

I don’t know if I have much of value to add to or reply to your second paragraph, but yeah that fixation is weird.

It’s a sequence of quotes from Fight Club

I mean, he didn’t really have much of a problem with accuracy - he fired a total of 1058 rounds, and those rounds or shrapnel from them injured 413 different people. Of course, many people received more than a single gunshot wound. He killed 58 (later 60) in ten minutes of shooting – effectively one person every 10 seconds. I think it would be difficult for a single person to injure or kill more from where he was standing with any weapon short of an RPG.

He was operating a significant number of his weapons on bump stocks. Bump stocks allow firing at a much higher rate than the weapons were designed for. Operating at a higher rate causes the weapons to overheat. Overheating causes misfires and jams (and inaccuracy and can permanently damage weapons, but I doubt he was particularly concerned about those things). He did have them all set up in a row and many on mounts. He broke out the overlooking windows of his hotel room before he started shooting. It seems he was shooting with one until it jammed and then moving on to the next rather than trying to clear misfires.

I don’t know about the lack of mental health care being the “main issue.” A healthy society wouldn’t be in dire need of such extreme amounts of mental health care. These mass shootings are a single symptom (among many) of a very complicated and interwoven set of factors that have brought us to this place. There is no single solution that will fix the problem, and the only way out of this mess will take significant investment and likely generations to break the cycle. But humans are greedy, and particularly in the USA, we only look for simple simgle-issue solutions that can have a measurable outcome (and be economically viable) within the next couple or fiscal quarters or an election term, at most. The solutions we should be implementing don’t work on that sort of time scale, and many will be very costly (in varying terms of both money and/or freedom)… So, we just don’t do those things.