Indeed, PLC's originated with GM calling for a programmable controller that could be used without having to completely re-train their large workforce of control engineers and technicians, who were already familiar with relays, mechanical timers, switches, and so forth.
Might be one of the few industries where I've seen visual hot-code reloading on-the-fly in production scenarios used at scale. The visual debugging of ladder is really similar to debugging tools we had, heck FBD[2] comes really close as well. Kind of an interesting covergent evolution of two different domains coming to very similar tools.
[1] https://docs.unrealengine.com/udk/Three/KismetUserGuide.html