Re: The one use
Fails due to confidentiality requirements:
I'm sure the person with the violent abusive ex doesn't want a public announcement publishing saying where she just graduated from, along with the names of all her classmates. It makes it too easy for the nutjob to track her down. If it's published promptly, he may even be able to go ruin her graduation ceremony.
Fails due to need to change the data:
People do change their name. E.g. trans people will want their certificate re-issuing with their new name after they transition. Also witness protection. Also, grades get appealed, degrees get revoked due to discovered fraud/cheating, etc.
Fails due to authenticity requirements:
To prevent a record of a certificate being faked, you'd have to have it digitally signed by the university. So how do you know which signing certificates are valid, and not something that the "degree holder" just invented? That implies some central organisation validating signing keys ... at which point the central organisation could just run a database of degrees, or a list of links to the university websites that allow you to check the degrees from each university.