Often the reason for having the user and password fields on separate 'screens' is to facilitate federated logon.
I.e. if someone has an account where they 'Logged in with Google' or it is connected to an IDAM solution like Okta or Duo, they don't have a password for the site so shouldn't be prompted for it.
As for the delay and any other nonsense, I'm not sure. Perhaps design winning over usability?