Don't be so hard on the guys in this video; it's easy to judge them after-the-fact. Who knows if they thought that something was likely to happen or not... Before the crash, was the driving just sloppy, or was it really *that* bad? Was the cameraman recording the white truck because he wanted to post a dashcam-style "bad driving" video, or did he think that something was likely to happen?
The cameraman at least realized there was increased risk in following a ****ty driver, so he was telling the driver to slow down, because he didn't want to get into a crash.
Most people make a judgement call as to whether it's worth calling the cops or not. I certainly do-- I see law-breaking dangerous drivers every single time I drive to work. If I called every ****ty driver in to the police, I'd spend my entire commute on the phone with 911 (and it's risky to be on the phone while driving!). The cops out there are already busy with the ****ty drivers that I didn't see! So I only call the cops when I'm sure a driver is dangerous, which is a couple times a year. So based on the what-would-I-do criteria, I'm not sure that I would've done anything, other than maintain a much longer following distance.
My past experience with drivers who are driving sloppily or poorly is that high-beam-flashing (which is illegal) and horn-honking gets no results. Maybe a finger, but the driving doesn't improve. And in the US, what if they're crazy/bad-drunk and armed?
In this case, if the Jeep driver was tired, they should've jolted back awake after nearly running a pickup off the road. My bet's that the driver was drunk. Delayed reactions throughout the video-- including sitting the green light.
Should the cameraman have called the cops? Yes, but it's understandable that they didn't.
Should they have kept a longer following distance? Yes.