That’s what they usually do. The assumption here is that due to the blackout or some other related issue the human drivers were unavailable.
However even if that’s not true if they have more cars than human drivers there’s gonna be a problem until they work through the queue. And the bigger that ratio, the longer it will take.
I guess that in a blackout they should just have the cars park somewhere safely. Maybe it'd be best to never have more cars on the road than assisting/available human drivers. As soon as no human drivers are available to take over for outage/staffing/whatever reason all cars should just pull over and stop.