ADC (Application Default Credentials) is a specification for finding credentials (1. look here 2. look there etc.) not an alternative for credentials. Using ADC one can e.g. find an SA file.
As a replacement for SA files one can have e.g. user accounts using SA impersonation, external identity providers, or run on GCP VM or GKE and use built-in identities.
one reason might be because with the fully opened window, the 'close window' cross is in the top right corner of the screen which is one of the infinitely large targets.