Alcohol has exeptionally bad ergonomics when it comes to intoxicants. Its strong effects on behavior and experience are wildly unpredictable, it has severe undesirable effects, it's stongly toxic, it causes morbid dependence and has particularly bad physiological and psychological after effects.
I think we won't get past the cultural issues in our lifetime.
Many cultures have 0 tolerance for anything outside of alcohol (and I totally get it when it comes to China for instance), and prohibition of drugs like marihuana was long used to target specific communities.
I'm not even sure if western cultures are still on the path to open to low harm drugs, do we have any research on synthetic drugs that have a change to become fully legal alternatives ?
There are very few cultures with 0 tolerance for e.g. nicotine or especially caffeine.
I'm not sure new drugs are even needed. There are plenty of existing drugs, and the vast majority are less harmful than alcohol. They would of course need legal and cultural regulation. There are also some ideas for new recreational substances like David Nutt's "synthetic alcohol".
Alcohol is one of the few intoxicants that you can legally buy almost anywhere in the world that is well regulated, has consistent dosages, and can engage in publicly. Being able to consistently source an unadulterated supply is one of its major appeals. Prohibition decreased consumption by as much as 70%.
The problem is that it's also responsible for a tremendous cost in terms of life, resources, and human misery. Drunk driving alone account for a quarter of 1.25 annual fatalities on the roads worldwide. I don't know how many people die from alcoholism, or have their lives shortened by it, lost wages, downstream effects of kids raised by alcoholic parents, etc... but it's certainly not a small issue.
So yeah the ease of getting the stuff and the social acceptance makes it popular, but is it a good idea? Drugs like caffeine, khat, and mild psychedelics have much more favorable therapeutic indices and a better track record in terms of death and illness, never mind be a lot less physically addictive and much MUCH easier to quit.
Alcohol is also very easy, which is a huge part of the problem. It's extremely easy to make, and to refine. Anything with sugars in it will easily ferment with simple exposure to the atmosphere and the ever-present yeast in it -- fruit that fall off trees when ripe will very quickly ferment, and our bodies themselves produce some amounts of it as part of metabolism. Once you have some alcohol it's also very easy to refine it to something stronger, you don't need distillation, just some method of removing the non-alcohol components of the mix, such as simply freezing the mixture to a temperature where the water is frozen but the alcohol isn't; You can take a bucket of low-% fermented fruit juice, leave it to freeze overnight, and take out the ice in the morning. Presto, you have a basic braga that's going to be much more potent. Alcohol is also very useful for a lot of chemical processes we rely on for many of our industries, so it will always be in demand industrially.
A lot of humans (and other mammals and birds even) also like the effects that it has, despite the unpredictability and side effects. It's just too good at smoothing out many social interactions in ways that we humans are fans of. It's also a very good source of easy calories that are very shelf stable and for the most part safe to consume even if the storage conditions were poor. Small beer was a thing for a reason - even a low concentration renders most pathogens inactive enough that it's mostly safe to consume.
Until we figure out some way to simulate the positive effects without the negatives, a Synthahol if you will, I don't think we'll be able to do better. And the Synthahol will need to be cheaper and easier to obtain than literally just leaving some fruit juice to ferment in a jar.
We can do better than alcohol.