Personally, I think there is a lot of truth to the autonomy, mastery, and purpose framework: https://en.wikipedia.org/wiki/Drive:_The_Surprising_Truth_Ab...

Another way to say it would be that I think it's about the job not aligning with people's intrinsic motivators. Doesn't necessarily require the job to be at all stressful.

When people don't have enough of those things, they get burnout. Some people get them from other parts of their lives, so they're unphased by lacking them at work as long as they make "enough" money. Some people just need less than others, for a variety of reasons.