Most likely because even non-alcoholic beer still contains like 0.5% of alcohol.

Unless it's a "0.0%" alcohol-free beer, and even then it might still contain a bit...

I bought hops-flavored sparkling water from a grocery store's beer cooler on a lark and, despite my attempt to explain the logic to the poor cashier, we both bent to the whims of the computer system and scanned my ID to complete the purchase.

There are other drinks that have trace amounts of alcohol, such as kombucha which is regulated to stay under the 0.5% threshold. Fruit juices will also likely contain upwards of the same amount, depending on how much they're processed.

I think orange juice can be up to 0.5% alcohol, and they don't check ID for that.