People will keep buying it regardless, prohibition didn't work, war on drugs doesn't work. All they are going to achieve with banning it is opening opp another black market.

The point is to encourage quitting and discourage new user. Alongside with stopping the depiction of smoking = cool in cartoons and movies and also advertisement of it, it actually helps, with smoker dropping globally.

There are also far more extreme measure, like stop people from able to even buy cig if they born after certain year, but that's the most a country can do, they cannot stop the sales of cig entirely because the withdrawal also kills.