I'm vaguely aware of what single sign on is. Though I don't use it, it seemed non-intrusive. The most you would see buttons to login through Google, Facebook etc.
Now some sites have an entire banner pestering you to sign in through your Google account. It has a big continue button that takes you to Google and the button to close is a small x in the corner. On mobile this banner takes up a third of the screen.
Why do this?
I only use Google anything when I have no other option. I don’t know what kind of arrangement companies have with Google, but running an SSO service costs money, so companies that don’t roll their own normally pay Okta or some other such provider.
Finally, a resident expert in single sign on.