- working in pairs, so there is social pressure, conversation, and two pairs of eyes to increase alertness and safety?
- doing shifts of 30 - 45 minutes at most [1] (although they could potentially swap back and forth with a co-driver)
- issued a dumb-phone for emergencies and searched for entertainment devices (it's good enough for Amazon warehouse staff)
- being monitored by the driver-facing camera, with training and termination for drivers who can't hack it
- monitored automatically for attention using eye tracking or other methods, with the car safely stopping if lack of attention is detected
- required to take over on a random, regular basis for a short period to keep them engaged and attentive (and obviously, the car keeps driving if they don't take over, but they are marked down)
Due to the boredom, it is an extremely demanding job, but the way it is being done is clearly not good enough.
[1] I can't find anything published about how long the shifts are, but I'm guessing they are longer.