Browser AddOn bypassing 2FA and/or Yubikey protection of 1PW Account-Management website. Why?

But wouldn't it make sense to protect the account-management website?

Your 1Password account has always been (and will continue to be) protected by your account password, secret key, and when it comes to new devices, the two-factor authentication code you'll need.

You would have to be already signed in to your 1Password Account within your browser (or in this case, the extension) to access your account management settings the way you're mentioning, so there's no security benefit to additional two-factor authentication when it comes to changing settings on an account.