I was told it was because you should be working during the day and only drinking after a day's work. But as far as I am concerned, those people can go screw themselves. If they like drinking way past a good bed time, being hungover the next day, and getting their sleep schedual all fucked up and being miserable in the middle of the day, fine.
I however, if I feel like drinking, pick an open day, get drunk in the morning(which is coincidentally when delivery food services are open), pass out by afternoon or late evening, and be unhungover sooner, and actually be able to function unmiserably the next day.