Check Wikipedia: “Staff Burnout: Job Stress in the Human Services” was published in 1980, and the Maslach Burnout Inventory was published in 1982.
> We don't bother collecting data on why people quit, or why people burn out, or what conditions eventually break them.
A quick search of academic literature shows this is not true.
Employers have no incentive to do research that would force them to spend more on employee wellness. I worked on enough team health surveys to know leadership has no interest in collecting feedback about the big known complaints that they aren't interested in addressing. They only want to hear about the small unimportant things that could help morale to cope with the big issues (unless they are forced to investigate serious workplace injuries, unsustainable churn/absenteeism or productivity issues)
That said employers/HR publish a lot of blog spam about how burnout is really due to employe's lack of self care.