Physical passports, in the same way as physical currency, have numerous mechanisms for reducing the ability to forge the documents.
So these documents can be checked locally without any form of communications to some central authority (which doesn't exist across national boundaries).
They have visible anti forgery like UV printed symbols and information, underprinted background text and patterns, etc etc.
So they are more "meaningful" than an offline smartphone with a passport app in that they do not require anything other than the officer's ability to see, feel and read the documents.
If being forgery-resistant is the argument for paper docs, a passport that identifies me using strong cryptography is just as forgery-resistant (likely more so). And we could do a cryptographic verification without a persistent internet connection. (Or can’t we?)
Even when there's no connection, no electricity, you get some modest layer of security out of "it's hard to manufacture a convincing fake passport if you don't have large-scale resources behind you."
What happens then with app-only passports? Do we close the border crossing entirely until the network is back up? Or do we rely on showing a QR code or NFC handshake that can't be properly verified? I'd think creating a fake passport app that reached those hurdles would probably be easier than getting access to specialized papers and printing technology.
A passport with strong cryptography would be forgery-resistant, however it is dependent on some form of PKI to distribute the public keys to every customs/border inspection point across the world, for every passport-issuing nation.
So these documents can be checked locally without any form of communications to some central authority (which doesn't exist across national boundaries).
They have visible anti forgery like UV printed symbols and information, underprinted background text and patterns, etc etc.
So they are more "meaningful" than an offline smartphone with a passport app in that they do not require anything other than the officer's ability to see, feel and read the documents.