Because it’s easier to get the ice cream, of course. From Brian Wansink’s Food Think:
One cafeteria tested (how much effort people will go to to eat ice cream) by leaving the lid of an ice cream cooler closed on some days and open on other days. The ice cream cooler was in the exact same location, and people could always see the ice cream. All that varied was whether they had to go through the effort of opening the lid in order to get it. Even that was too much work for many people. If the lid was closed, only 14% of the diners decided it was worth the modest effort to open it. If the lid was open, 30% decided it was ice cream time.
Some readers may wonder why a store owner would ever leave the lid on an ice cream freezer open? Would the extra cost of the energy (not to mention the general environmental unfriendliness of such a strategy) be worth the extra ice cream sales? Maybe not for a typical freezer. But Wansink says there are some in Europe that keep ice cream frozen from the bottom, allowing owners to lose the lid. Any readers seen or shopped at these freezers before?
Hat tip: Tom Vanderbilt.