The 18th amendment says "the manufacture, sale, or transportation of intoxicating liquors within, the importation thereof into, or the exportation thereof from the United States and all territory subject to the jurisdiction thereof for beverage purposes is hereby prohibited."

Why prohibit only the manufacture, sale, or transportation, but not actually make drinking it illegal? Why not include the consumption? Was it because they knew it would be too hard to enforce, and if so why do it in the first place?