That's certainly one of the thoughts that I had originally! But if you look at the details, perhaps it will become a bit clearer for you: Each of my email accounts are themselves protected by 2FA, so "those accounts" are not just "protected by regular passwords".
You can have email accounts with multiple email providers, e.g. gmail, outlook, etc. So, depending on how your email account gets compromised, this gives you additional layering of security. If mail provider X has a security breach, no big deal, because you also are using provider Y.
More generally, this can be seen with any factor in authentication, i.e. a claim. If any claim X is compromised, by any particular attack vector, then you also have Y, Z, etc. in play, depending on your security vs. convenience configuration.
And as I stated, email is only one of the avenues used to provide evidence for a claim. In the future, Oauth(2) tokens, sms, etc. The point is that it's an extensible mechanism for genuine MFA, instead of hard-coding in the "2" in 2FA. And that diversity is where the "real power" of multi-factor authentication comes into play.