At least with all the porn bills I've read, it's illegal to retain the information.
By the way, Pornhub actually has a preferred technical solution involving "device attestation". It's only marginally better than the snake oil the AV industry wants to use, and I don't like it, but they have said they'd stop objecting if something along those lines were standardized.
They just don't want to have to deal with a patchwork of mutually incompatible stuff (a) that's totally ineffective, (b) that leaves them either handling everybody's ID or dealing with questionable contractors to hold it, and/or (c) that leaves them having to convince the users to trust them or those questionable contractors with those ID images.
It doesn't actually. Third party zero knowledge attestation works just fine. Think through the cryptosystem. It's possible for an authority to verify an ID for a given name and target site without revealing the former to the latter of the latter to the former