When I worked in electronics manufacturing, production engineers were frequently out on the floor. Common issues were:

• a machine was placing a part incorrectly
• assembly workers couldn't understand blueprints
• materials were getting damaged in a process that shouldn't have been a problem
• a custom design tool/rig was not acting like it was supposed to
• there's something clearly wrong with a process (like it was designed for one person and not an assembly line)

If anything major (or potentially major) came up, production completely stopped until the problem could be assessed by an engineer. Assembly workers weren't allowed to fix things and they couldn't estimate the cost of continuing to run a job with defects. Our engineers didn't work 2nd/3rd shift though, so every time a job had issues we'd have to drop it and leave it for first shift. A downed line for 8+ hours is a LOT of money and for a bigger company would warrant calling someone in.

(I think the bigger issue is not "work ethics" like the article said or "need" like you said, but that the US has rules and pay requirements for on call employees)

Call me an engineer and you need to pay me a lot more though so that doesn't really make sense.