Where did you get the idea 'global' from?
Have you seen Peer DIDs? Most specifications advise you to create limited purpose identities. Use a widely known one when it suits you, like a LinkedIn profile, or Twitter page.
Exactly. DIDs don't need to be global identifiers. I can create multiple DIDs. Maybe one of them gets issued an identity VC. When required I may use that DID to prove my identity, otherwise use the other DIDs.