I agree with your assessment that most people don't have a choice not to work, but I'm not sure I find the metaphor to be a compelling case for it. In both the hamster scenario and real life, there's a choice to work or not which has some variable effect on the likelihood of getting fed, but due to the effect of the hamster's work being minuscule compared to a human's in terms of influencing whether they're fed, the choice to work or not is easy. This might just be one of those things where I tend to interpret things too directly, but the idea that "choosing not to run on the wheel is like choosing to be happy" feels like a way less obvious interpretation than "choosing to run on the wheel is choosing to work".
The metaphor is that there is some baseline you must do to get fed each day / live. For the hamster, it just happens by nature of living in a cage - but it's not pleasant ("will I get fed today?" being a constant concern) For people who work low income jobs, it's similar and the cage is the job(s).
Both hamsters are in a cage (job to live), and yes - when one is more noisy, runs more, etc. (works real hard) the owner notices it more frequently and gives it food, treats, etc. (better pay)
