In modern factories, all equipment is automated and extensively networked. In many cases, the wiring is several dozen to several hundred meters long, making it easy for a potential difference to occur between grounds (making it easy to be affected by lightning surges).
Industrial robots are also sometimes controlled remotely, and when equipment malfunctions or is damaged due to lightning surges, there are concerns about not only repair costs, but also delays in shipments and lost opportunities due to temporary suspension of operations.