I know that while I am always prepared to pull my items off (belt, laptop, jewelry, etc.), whether I do so before I am in line or during depends on the length of the line. If it is long, then I pull it off as I move along. I will say that since I have been traveling weekly, I am better about pulling the stuff earlier rather than later in the line. Perhaps these folks are thinking of other things than security as they wait in line (meeting at other end of flight, family issues, etc.) and don't think about it until they get closer. I don't think that anyone wants to keep people waiting on purpose. I know that if I am distracted as I wait, I pull myself to the side when I get to the table and let others pass if I'm not ready to not hold people up.

On the flip side, it would be helpful if they had the bins staggered at the tables so that you don't have to wait in line for that! I find that I spend more time waiting for a bin than I do 'stripping' for security!