Alcohol use dropped substantially during the same period with no preceding significant change in its legal status.
Except for:
Plus the court's definition of liability has been expanded in civil suits to include anyone and everyone who had any contact whatsoever with the drinker. Plus the penalties have increased.
Legal status aside, there are many other reasons (price, taxes, social stigma, etc.). Don't let Know your rights (aka MrLeRoy) define and limit the scope of the argument -- a favorite tactic of his.