2 reasons:1. It's a macho man thing, a throwback from the 80's. Sleep is for wimps, etc. Also, if they're paying you big bucks, then they expect 100% dedication from you. They're buying your life, not renting your time. 2. It's an oligopsony. If you challenge the status quo - well, there's plenty of insecure little academic overachievers out there who will happily take your place and work all hours of the week. What do you think of the above?