Something I didn't see in the other comments is users who are using the startup's service for work, as an employee.

Why wouldn't you choose the simplicity of "sign in with Google" if your work email is on Google Workspace, using the entire Google suite of business tools for everything (gmail, chat, meet, docs, drive, auth, etc) any everything you do at work is known to Google anyway?

Making an email/password account with your work Gmail is just extra steps, one more password to store, and perhaps the inconvenience of one more 2FA thing. Google gets the same information either way.

Similarly why wouldn't you choose the "sign in Microsoft" if your work is all in on the Microsoft suite of business tools (teams, office, onedrive, auth, etc.) and everything you do at work is known to Microsoft anyway?