It indeed is a luxury to be able to take a year off at will. Big reason I can think of is financials.
In my opinion, burnout is a problem only faced by people who can afford to do so. I am not saying everyone doesn't face burnout, they probably do, but not everyone can afford to take a sabbatical, dip into savings, indulge in a hobby etc. There are many people who don't earn as much as a silicon valley engineer, have low savings to dip into, and perhaps even have/inherit debt - Making rent and being able to afford essentials takes priority to dealing with burnout in such situations.
In my opinion, burnout is a problem only faced by people who can afford to do so. I am not saying everyone doesn't face burnout, they probably do, but not everyone can afford to take a sabbatical, dip into savings, indulge in a hobby etc. There are many people who don't earn as much as a silicon valley engineer, have low savings to dip into, and perhaps even have/inherit debt - Making rent and being able to afford essentials takes priority to dealing with burnout in such situations.