If you were cited for going 68 in a 25 you can point out that you were on the highway 10 seconds before and 10 seconds after the incident, and had no way to get to the access road under the highway. If your vehicle decided you were speeding and slammed on the brakes in the middle of the interstate, you'd need a much more reliable system.
If your relationship with your employer is dehumanized to the point where these reports, reviews, and penalties are interactions with an uncaring piece of software, that's a different problem.
Or:
The Amazon manager is either going to fire the employee after a number of reports or keep the reports in their back pocket to use when they need an excuse to fire the employee.
I don't know about the Rivian, but many driver monitoring systems are aftermarket retrofits, not vehicle manufacturer parts. The driver monitoring system is just a fancy dashcam with cloud uploading features, and a bunch of people in a low-income country manually labelling video clips.
Or to put this another way:
We have a system for perfectly knowing what the drivers speed is. We also perfectly know what the legal street speed is.
Instead of limiting the drivers maximum speed to the legal street speed, we instead just tell their boss?
Looks to me like Amazon wants their drivers to violate the speed limit but then also want to have a record of when they do so they can fire them for cause.