> Why wouldn't they?
They most likely weren't allowed to keep it past the verification per GDPR art.5. Once the passport has been verified for whatever purpose they needed it ("age verified to be > 18yo on 2026-06-12" or "identity verified to be XXXX YYYY"), there is no legitimate use for the passport photo and details anymore, and they should delete it.
(I'm naive in this area, but..) I wonder if the various "proof of age" laws coming into play will clash with the GDPR in insidious ways. Like requiring identity providers to hold definitive "proof" of why they made an assessment rather than merely proving and discarding. I assume/hope there is some cryptographic way to do this rather than hang on to passport and ID images, however.