If it was so simple, were you the one repairing the machines when they broke?
Yes? Fixing machines is a part of working on a production line. If it's more serious than that then you call the mechanics. If they can't fix it then they stop using a machine from the 70s and buy a newer and equally unreliable equipment.
Getting the machines up, running and maintained is the hard part. Being a button masher when the machines are working is the easy part. There are also many more complicated industries than the one you worked in, for example almost any chemical manufacturing plant.
I don't want to be too specific here but the factory I worked in produced pharmaceuticals. Medicine, syringes, etc. Like I said, the most complicated and technical aspects of the job really pale in comparison of the challenge of logistics.
Your example is like me saying that a car is simple because I know how to drive one. It is so simple that I have someone else repair it when it stops working.

It's actually pretty similar because it's not outside the realm of possibility for someone to actually work on and fix their own car if it's something minor. The same goes for machinery on a production line.
Of course it depends. I'm pretty sure pharma is light industry while chemical is heavy, but regardless, something being complicated doesn't mean it's impossible to manage collectively.
I'm on some sickle-hammer shit
Collective Bruce Banner shit
FKA: #FF0000, AKA Mistake Not My Current State Of Joshing Gentle Peevishness For The Awesome And Terrible Majesty Of The Towering Seas Of Ire That Are Themselves The Milquetoast Shallows Fringing My Vast Oceans Of Wrath