Few reasons, actually. If they are teens, they are easy to hide, and generally only need a couple to get wasted. If they are adults… They are cheap, and it is easier to work up enough money for a small bottle to stop the DT’s, then work on getting money for getting properly drunk. Also a lot of places are only allowed to sell the small bottles of full strength liquor, and often alcoholics have been banned from most of the places that are licensed to sell all alcohol, or they have long since lost their driver’s license, and the only place that sells in walking distance is a gas station who can only sell half strength liquor, or these small bottles of full strength.