Adults can be prosecuted for selling alcohol to minors (I mean, they can be prosecuted for selling drugs to other adults even). Because there is a physical handoff, there is risk in doing so, and thus there is high friction, which we deem to be sufficient to curtail the risk.

No such friction or accountability can possibly exist when we're talking about a bunch of yubikeys, unless we attach identity to them (THIS IS A BAD IDEA).