I am wondering why at the first place iPhone allow to sign in with Google Account and other accounts under MENU : ACCOUNTS & PASSWORD there, but cannot restore from Google Drive (from Google Account)? whats the sign in google account for? for contact list only?

I can see alot of ppl said there is no way to restore whatsapp from google drive, besides saying via 3rd party app, not even apple self-app "MOVE TO IOS".