Being carded in person can be and until recently* was done with the identity being revealed to only one person who was likely to forget it shortly after purchase.
Being "carded" online all but requires that the ID be stored at least for a short time and typically indefinitely, with no guarantees that it isn't being copied by malicious actors or used for privacy-hostile purposes.
If we can adopt a standard way to verify our ages without presenting our identities or at a minimum have our identities stored relatively locally, say, by someone akin to your friendly neighborhood Notary Pubic, it would eliminate the "big juicy target for hackers and governments" that are today's identity verification systems.
* Old school, still in use in many places: Look at IT, look for obvious signs of ID being fake or tampered with, let person in, forget about it. New school, here in some places and coming soon in many others: Run IT through electronic verifier that phones home to the government that issued it for verification, which has similar privacy risks as online-id-verification.