Side topic I hadn’t considered... If you don’t use 2FA on your google or Facebook account, how are delighted authentications any better than password reuse? They actually seem worse / less secure.
You get to set permissions on a per-app basis, so that's a lot less access than going them your password. And if they abuse the access you give them, you can deauth just that app instead of changing the password and breaking all the apps. Edit: I think you were asking about the other direction. It's still not as bad, because if you are sharing passwords and any service was breached, all you services would be exposed.…
But if you lost the gmail/Facebook login you also loss all of the sites you used. Classic single sign on issue.