They want to make some money out of it. Most of the things that got banned increased their values and I truly believe illegal stuff has more circulation than legal one. Just remembering when China banned Bitcoin it raised in price and popularity.
It seems to me that such a comparison is inappropriate in this case. They could just raise the price, without prohibition. But the government has decided to take it that way, so they want to do to get rid of alcohol. Now it will be sold illegally