I spent a bunch of summers moving furniture, and often driving a tractor trailer. I was fully licensed, yet very inexperienced. Clueless. Had no business being behind the wheel. I was a college kid. I had three fires over the course of three years, and countless other "issues".
I would be one of those guys riding the brakes far too much. Driving too fast, etc. NO question in my mind. As others have mentioned, the maintenance on some of this equipment is pretty lax. I once flatted the inside tire on the rear of a trailer. I didn't see what I should have in my mirrors. The flat over heated, melted, and essentially was wedged under a wooden floor/deck which was saturated in oil and grease {Furniture trailers have oak floors}. Flames and smoke ensued. Luckily we had more that out normal supply of extinguishers on board, and we had help pull over fast. The load had smoke damage and no fire damage. When we looked at the other inside tire, it was something that should have never been on the trailer.
Had another trailer burst into flames, when we had a loose set of chains sparking like crazy right near the "fifth wheel" , where the trailer was again saturated in fluids. Laziness and lack of attention to detail. That one took off fast. The guy with me, who was in charge, pretty foolishly reached with gloved hands {took a big risk...minor burns}, and we uncoupled the trailer like lightning fast, and I pulled the tractor far ahead. The trailer was pretty well incinerated. Sad. All of a family's belongings.
I think that a lot of these things are traced to inexperience, some laziness, poor maintenance, poor choices.....and some bad luck. But yes, this is a business that I'm afraid has far fewer serious professionals than it once did. A lot of companies "cheap out." The last two times we moved, I was pretty astounded at the equipment and employees.
The comment that really hit home with me was @segbrown saying it would have been a disaster if it happened in the tunnel. I have been in that tunnel a fair amount, have observed some of the rigs around me, and the vehicles in general, and I'll admit have been uneasy at times. Particularly when traffic is crawling through there, let alone stopped for some reason. Luckily not that often, I guess.
In fact, I've been blown away by what people drive on that highway, in the winter, in snow. Been there enough over the past five winters to not be surprised by much, but it's just "wrong."
