I'd chalk it up to constant job insecurity, too. There's a glut of unemployed since the last recession, and few places to put them, meaning that people hang on to whatever they have with an iron grip.
Oh yeah, and no legally mandated paid sick time, or vacation time. That'll add up to burnout ultra quick. There are also very few controls on how many hours they can physically make you work, and very few controls on how/when they can schedule you to work.
Gotta work indefinitely for less and less with no real control over when or for how long you work, and you're a few mistakes from being cut loose. For many people paid by the hour (and quite a few salaried people too), that is the reality. Did I mention that in the US people get their health insurance from work, vastly increasing the stakes of holding down a job? Not being able to afford a doctor when you're unemployed adds a lot of stress when you are employed-- and that's assuming you don't have kids.
I guess exercising on the job is a pretty big improvement, if those poor conditions are what you're facing. I really wish that more places would actively set aside time during the normal 8 hour (including an hour for lunch) workday for exercising.
Really, this whole country needs to have a sit down and re-enshrine basic equality, basic labor laws, and basic decency. This process will be like pulling teeth, because the capitalists at the wheel consider workers rights to be anti-profit. It probably won't happen unless someone like Sanders gets elected, to be blunt.