People run marathons for fun. They fight each other for fun. They risk their life to have fun by climbing mountains. But nobody works a steady job for fun. That's because its real hard work.

People love to do activities where their efforts and rewards have a strong correlation to each other. Athletics are an activity where hard work pays off. That’s rare at a job.

Untrue, fair amount of old folks are so workbrained they keep a job after retirement as a hobby. One guy I know put in ridiculous hours because he would be at the bar otherwise.