Because this data doesn't exist on Apple servers, and what does exist are a bunch of randomly generated identifiers. Have you read the proposal at all [1]?
It's not clear from these specifications on how the rolling IDs are associated with a single user after a diagnosis is made, and whether those keys are interlinked. While this explains the phone-to-phone model it does not explain the other half of the system from what I can tell.
I think by design they're not meant to be associated with a single user. A hospital would publish all id's of users that have found positive with covid and each other individual user's themselves will see if they have been in contact recently with one since they have saved all id's they've seen recently
Could network analysis be used to deanonymize these rolling ids? I remember reading that network analysis easily deanonymizes blockchains. Seems same would apply to rolling ids.