Password managers are a poor substitute. They don't work well and they are not consistent across websites.
Let's say you're part of the marketing team and need to sign up to some ad platform or do a one-off order for branded goods. They will most likely not support SSO, and even if they do you won't have the necessary privileges to actually set it up.
Password managers are a poor substitute. They don't work well and they are not consistent across websites.