Bad interpretations of the law, business valuation metrics, and more. If I have a week where I'm working late into the evening, and the next week is slower, why would I feel bad working fewer hours, versus sitting in my office chair posting on CB until the bell strikes 5:00 or whatever? Note that my job offer didn't say anything about the particular hours my butt should be in the chair. I do all of the work the company has asked me to do and then some. My CEO doesn't care how many hours I sit there, as long as I'm responsive when he needs me.

Note that I had another boss who would rage if you left before 6:00, no matter whether you had any work to do or not. She didn't care how early I arrived, I was not to leave before 6:00. She would regularly call or walk over to our offices at 5:50 or later with non-urgent questions or comments after not speaking with us all day. It was unpleasant working for her. My total hours worked were reasonable for my field of work, but it was dumb sitting there into the evening on slow days to feed her need for power.