Many people use the same password for their email as they do for their exchange accounts, and some exchanges will allow password reset emails to be sent to the same email which is being used to 2FA. Therefore you are reducing the security of your exchange account from 2 factors to 1, since both factors can be compromised with access to your email.
Thanks for quoting the above lines. It is actually risky thing to keep same password to exchange and gmail or having same password to multiple account. If the password is hacked or know then all of the accounts are gone(I mean as you said reduced to one factor authentication). And in this case if we have a weak second FA like SMS or email confirmation then it is like we have risked our accounts.
