How can the monitor do other things if he is expected to have full situational awareness at a moment's notice in case something goes wrong, when you have no idea if or when that might happen?
All the studies say this is actually more dangerous, which is why Waymo abandoned L3 development years ago when they discovered their safety drivers were falling asleep at the wheel. And there's the infamous Uber death which is well documented and analyzed.
That's the difference. In an autonomous urban driving environment a monitor is expected to have full situational awareness at all times because driving in cities is a hugely complex process. A truck driving 1,100 miles on I-80 would not need to be monitored as closely, if at all, because that driving process is far simpler. This kind of highway driving accounts for the majority of over-the-road freight.
"Monitor" might be a misnomer, here, in that the monitor isn't expected to be actively watching what the truck is doing; rather the monitor would be expected to respond to infrequent issues and maybe handle off-highway driving to and from shipping and receiving facilities.
I understand the idea of having drivers take over in dense urban areas, and letting the truck drive itself along the highway between cities. But this assumes the truck is capable of safely navigating along the highway with zero human intervention. An inattentive driver/monitor is no better than no driver when something unexpected happens and requires a sub-second reaction. If they can do that then they're in business, but I am skeptical.
All the studies say this is actually more dangerous, which is why Waymo abandoned L3 development years ago when they discovered their safety drivers were falling asleep at the wheel. And there's the infamous Uber death which is well documented and analyzed.