Automated food production is very much simpler, because you're usually only producing one food item at large scale. That's the super easy stuff to automate.

Automated driving is more like a fully automated chef, that can create new dishes from what his clients tell him they like. Without the clients being able to properly express themselves. That's a lot more complicated than following a recipe.

Difficulty of automation goes roughly trains < planes << cars.

Automated trains are simple, but don't provide much value. Automating planes provided value because it's safer than just with human pilots. Automated cars are a different league of complexity.