Burnout is from people doing tasks that bring little fulfillment for most of their one life on Earth. If you have 1 free minute in 1 year, it's irrelevant what you do on that 1 free minute. This is an exaggeration, but it's to show my point. People want to be spending time doing things they like. 40 hours a week is way too much time spent doing the opposite, regardless of what you do outside of those 40 hours.