Certain tasks are cheaper done manually. Also, certain technology is not ready for implementation in manufacturing environment. As an example, all automated optical inspection at my industry is still followed by manual visual inspection. Machine still has lots of false alarms; identifying non defects as defects.

@@BKNew2022 Well answered, not all the processes must be automated also automation creates new problems

They answered it in the video introduction. This factory has frequent model changes and those have different manufacturing requirements. They contain similar steps, but different sizes, screw locations, screw sizes, etc. This is the bane of automation. So they've automated the core steps, but left other to be done manually.