It's good money for people who don't have proper higher education degrees. I know many blue-collar workers making well over what some engineers make. But plant life is tough... Repetitive tasks in loud environments, frequent overtime, etc. I'm sure many operators hate the smell of lubricants.
Repetitive tasks are the least of it, usually.
The most frequent complaints I hear about are the loud noises and the working in shifts. At my factory they have to work in 4 shifts: the shift is 8 hours, one week it's the morning shift, the fallowing week there's the afternoon shift and then there's the next week with a night shift. The 4th shift is 12 hours on Saturday and Sunday, 2 weekends, with the Monday to Friday being considered free days, but many of them use the "free week" as a time for getting extra hours and money.