There's a much more mundane reason why alcohol and tobacco are still legal: we're sitting on millions of addicted people.
From the cradle addiction to the actual grave, every step along the way feeds capitalism. Government fully supports that because it also meets the needs related to resource management. Addicts don't cost money. They make money.
Remember what happened during the prohibition era? It turned out that addicted people are willing to help destroy society to get their fix. They'd rather pay the Mafia, an organisation bent on killing folk and subverting the rule of law, than try to do without their fix. The result was that the prohibition era basically caused most of America's organised crime and we're still paying for that.
The reasons for Prohibition never coming back again are a bit different today than when it was introduced. Alcoholism was conveniently labeled as a "disease" many decades ago. Why? So that the growing Medical Industrial Complex could obtain a massive benefit from it, backed by insurance companies who will now cover you to treat this new affliction. Pure capitalism drives the legalities around alcohol today, which will never be denied no matter how many MADD mothers march. Alcohol is now a $200 billion dollar burden on society, which drives a lot of money into the pockets of those lobbying to keep it legal.
Addicted people aren't really human in the normal sense of the word, and if you forget that, you'll pay for it.
In a capitalistic society controlled by pure unadulterated greed, an addict is nothing more than a reliable customer.
Even countries which are trying to address these issues are doing it slowly, one baby step at a time, because they must ensure that at every given step all the addicted non-humans won't suddenly go off on one.
Controlling the addicted zombies to keep the horde at bay is a cute theory. I prefer to accept the fact that resource management is an obligation of every government. The baby steps are political bullshit pandering to put forth the image that we are a civil society who actually gives a shit about not creating addicts while maintaining profitable legislation that unfortunately creates addicts.