SSO to me exists for the sole purpose of keeping you locked into their platform. I have a "professional" email that I previously hosted on google with gsuite. I used that account a few times as SSO.
Now even though I have moved that email off of google, I continue to pay gsuite just so I don't loose access to that account and anything I logged in with it.
I have made every effort to remove google from my life as much as possible, but that account remains thanks to SSO.
Some SSO services don't give you an easy way to change how you login so you could be stuck.