Imagine the following scenario:
An evildoer hacks into my e-mail account, michaelt@example.com, creates a salesforce.com account (with a password). They delete all the e-mails about account creation.
I discover the hack and change the passwords on every account I know about - but I don't know about the salesforce account (in fact I don't have the password to it) so the hacker retains access.
Should the hacker be able to visit gitlab.com, hit the log-in-with-salesforce button, and get access to the michaelt@example.com account?