If you're storing passwords for the non-SSO option then you're hurting yourself as well as your customers, because storing passwords is a massive security and operational headache. If your limited SSO options, before charging the SSO tax, are "social" (e.g. Google) logins, then you're letting BigTech in between you and your customers.

I'm all for price discrimination, but SSO is the exception, because the alternative is too expensive.