One benefit of automation they also failed to consider is customization. All sorts of exotic designs, configurations, adjustments and test iterations could be made. Hopefully with a standard base so they can be repaired or swapped out later, but the less human training that's required to get an assembly line up the faster you can change and improve it
Another aspect is potentially repairs itself. If every part can be added by a machine, they could later be removed and swapped out as part of the maintenance cycle too
Programming an automated line to build a car (or any other product) in a different way is a tremendous amount of work, since all of the motions have to be exactly right. Usually customization weighs heavily in the favor of humans, who can adapt much more easily to parts that are different.
Also, an automated production line isn’t going to be any use for repairing cars, all it can do is bolt them together.
These aren’t some kind of AI robots. They are mechatronics that are programmed to follow very specific toolpaths. Reprogramming them by even a few millimeters is a monumental task, and to test them, you have to try to build a car ...
Another aspect is potentially repairs itself. If every part can be added by a machine, they could later be removed and swapped out as part of the maintenance cycle too