Nowadays when you want to register for a new service
like opening a bank account, you have to prove your identity to the service provider with your ID card and if you come back for a service each time, you will need to do it again, either by presenting password or other credentials. So, the repetitiveness is not only the weakness of Centralized Identity with a single domain (or even multiple domains) but also privacy issues, data leakage, and risk of sovereignty.