Depends what country you're in. In most of Canada grocery stores do not sell liquor.

But at any rate, they're going to ask for ID when you buy it. Children can't access it.

It’s a lot easier to ID-gate food based on whether it contains some amount of a substance (alcohol) than it is to ID-gate media.

For extremely explicit stuff, sure, the adults-only line might be clear for a lot of folks. But other stuff is not as clear cut: if media describes sex at all, is it adult? Even Supreme Court justices have trouble defining in this area.

…and all of that is ignoring the elephants in the room: whether or not explicit media even should be restricted for non-adults, the fact that there are highly variable and localized levels of people’s preparedness for adult media (even more variable and subjective than developmental cutoffs for alcohol sale), and the abundant historical evidence that attempts to draw an acceptability/adults-only line in subjective areas like this are inevitably extended to provide cover for political agendas (e.g. homophobia).