Before Tesla, I remember reading an article that Mercedes-Benz removed a bunch of robots from their assembly line and put people back. For them, the issue was about variation in products. For example, a single line of cars for them might come with one of several different mirror assemblies. Making a seperate line for each permutation of possible trims and options is inefficient, and the robots weren't adequately able to tell apart similar but different parts (e.g., basic mirror, mirror with the turn signal, mirror with the turn-signal and auto-dimming, sports aerodynamic mirror, mirror with chrome accent, etc.) on a car-by-bar basis as compared to humans.
Notice how Tesla has almost no variation among models, other than paint color, interior color, and battery size.