Since when is it unacceptable to draw?

I work in a space where we man computers for 24-hour shifts, and most of the hours nothing happens. I’ve found that at work, it is acceptable to watch youtube, check facebook, study for a class, listen to music, and generally toss off, but for some reason not to draw on the job. I am a comic artist on the side, and find it is a good outlet for stress and something I can do passively while other things happen. Why is it that so many people at work frown on drawing?