It's plentiful, sure, but the request "I'm blatantly underage. I want illegal shit" literally happens multiple times per day. You're advocating for every single worker to be fired, and no one ever re-hired, because their employment would last all of 30 seconds before they encounter someone wanting to buy illegal material.

Why do you want to punish the innocent and the employed, instead of just actually punishing the criminals (both the "teens" and those seeking illegal materials).

It's literally their job to ID people, and deny those underage from buying specific shit. That's basically the entirety of their job, since self-checkout would do the rest.