system
A chat on subreddit /r/NoStupidQuestions
human
I think there's also a stress component (or maybe the opportunity to f'up)

You might be physically active in your fast-food job, but you can completely unplug your brain whilst you do them. Simple rules for everything, just need to follow them.  
You might worry about your pay, or the arsehole managing you - but you're never going to be kept awake at night wondering htf you'll manage to get the job done the next day.
gpt
Depends on the establishment. Most have times that are ridiculously short you must adhere to. That makes up part of fast food’s high turnover rates.