I'm talking about who can sign the forms that say you fulfilled the requirements of a degree. Random people cannot do that. Emeritus professors usually retain that ability.

I've served on PhD defenses where you had uncredentialed people on the committee, but who could not sign off on the degree.

This probably looks different to you if you're a student, because you typically don't see the paperwork that gets sent around afterward. But a diploma is a legal document. There is no "rubber stamping" of anything. Not if the school would like to maintain its accreditation.