As I understand it, the why is that they were super-heated by LOTS of slipping. Not just a little, like at a stop light, but more constant slipping that built up more and more heat. Initially it was reported that the one that wound up blowing apart, cutting hydraulic lines, and causing a fire, had hit 1200 degrees. Later that appeared to be revised to 1100. There is no pressure plate in the world in a production car that can tolerate that kind of temp, especially for any extended time. That's what weakened the metal and caused it to fracture. I doubt that these clutches ever get much beyond 200 degrees. If they do, say when slipping a lot like pulling a boat up a ramp, it wouldn't be too much higher and it would be only for a short period and would cool down quickly right afterward. These kept slipping and slipping, the entire time the Jeeps were driving, as I understand it. That constant slippage due to the clutch plate only partially engaging, built up more and more heat.Mine was a "Bad" clutch, did not engage properly at all, yet it took a ton of abuse and was not slipping at all when I replaced it. I agree fully with your 1.2.3.
Still, why did any of them ever come apart? I believe official tally is under 10 catastrophic failures out of 35,000. But still, why?
They're probably beyond 50k now in sales and the highest number of pressure plate's effected appears to be around 12, but the pressure plates could have come apart in some without blowing out the bell housing. I only heard of two that I'm pretty certain came apart and busted through the bell housing. One of those was the one that cut a hydraulic line and burned his Jeep to the ground. They gave him a new Jeep and I'm certain that one of the conditions was that he stop talking about it. That's just standard procedure and is directed by attorneys. Not unique to FCA/Stellantis. But they did take care of him, last I heard. Oh yeah, I've also not heard any reports of any injuries.
It is really VERY hard to determine the actual number, but if it were significant, that would not be hard to see. You only get an idea of the number when the NHSTA or another federal agency is involved. They only release that info when they have to. Sometimes they only hint at it. But everything I've read or heard points to a very low number, which is around 12. If you try and be safe and double that number you are still only looking at 24 out of 40k plus. That's 3 ten-thousandths of a percent. That's why we don't have forum members posting pics right and left of their blown out bell housings or telling us their pressure plates and clutches were replaced under warranty. (Worn out clutches don't necessarily indicate the problem, however, for reasons discussed earlier.)
And again, a good number of clutch drivers wear them out early. And it might not be the owner. If you let someone else drive your Jeep, without you present, as I do, you won't know if they were excessively slipping the clutch unless they tell you. I did see my brother in law smoke the hell out of mine and my wife told me she did the same. Both were in either 3rd or 5th gear by mistake. That's why I like the dash indicator. Not for me, but for others. My neighbor described my wife's episode as "like a destroyer laying down a smoke screen!" Fortunately, mine shows no sign of a problem. I don't think either did it for very long before realizing their mistake. It sure pissed me off, though. But I kept that to myself.