Because it's hard to get any laws passed, much less a law that tackles two major things (tobacco and alcohol) at once
In most US states the sale of alcohol is already much more restricted than the sale of tobacco.
You can walk into any 7-11, convenience store, or gas station and buy tobacco. In most states, this is not true for alcohol.
Also, tobacco vape use is much more addictive and somewhat more concealable than alcohol. People can generally tell or at least suspect you've been drinking; people generally cannot tell if you just vaped 10 seconds ago in the bathroom.
It's far from ideal and you and I would certainly not design a country from scratch this way, but legislation (at least, ideally) deals with things as they are and not with an imagined tabula rasa state of affairs.
